feat: full-basin 2024 flood replay with clock and demo indicator

The replay now drives the entire map from a 120 kB all-station snapshot
(static/flood-2024-all.json: 649 hourly frames x 16 stations of level +
discharge, forward-filled on an aligned grid):

- station markers recolor/resize per frame from historic discharge
- river segments restyle per frame (color/width from the same
  nearest-gauge grading as live mode)
- flood zones flood/recede from P.1's historic level
- a large clock overlay on the map shows replay date/time, P.1 level
  and total basin flow
- the LIVE DATA pill switches to an amber '2024 REPLAY' (or
  'SIMULATION' for the demo_level/demo_rise hooks) and back on finish
- replay end or stop restores the live view via a full dashboard reload

Replaces the P.1-only snapshot (flood-2024-p1.json removed).

src/static/dashboard.html

@@ -50,6 +50,8 @@
             background: var(--mint); color: #146644; font-weight: 750; font-size: .8rem;
         }
         .live-dot { width: 8px; height: 8px; border-radius: 50%; background: #22a66c; box-shadow: 0 0 0 5px rgba(34,166,108,.12); }
+        .live-pill.demo { background: #fdeeda; color: #9a6200; }
+        .live-pill.demo .live-dot { background: #e6a23c; box-shadow: 0 0 0 5px rgba(230,162,60,.15); }
         button {
             border: 1px solid var(--border); border-radius: 11px; background: white; color: var(--ink);
             padding: 10px 14px; cursor: pointer; font-weight: 700; box-shadow: 0 3px 10px rgba(22,52,62,.05);
@@ -127,6 +129,14 @@
             width: 26px; height: 26px; display: grid; place-items: center; font-size: 19px;
             filter: drop-shadow(0 3px 4px rgba(5,43,58,.45));
         }
+        .replay-clock {
+            position: absolute; z-index: 650; left: 50%; transform: translateX(-50%); bottom: 20px;
+            background: rgba(19,43,53,.9); color: white; padding: 12px 26px; border-radius: 15px;
+            text-align: center; display: none; pointer-events: none; backdrop-filter: blur(6px);
+            box-shadow: 0 12px 30px rgba(9,30,38,.4);
+        }
+        .replay-clock strong { display: block; font-size: 1.65rem; font-weight: 800; letter-spacing: -.02em; white-space: nowrap; }
+        .replay-clock span { font-size: .78rem; opacity: .85; }
         .forecast-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(215px, 1fr)); gap: 10px; margin-top: 14px; }
         .forecast-station { border: 1px solid var(--border); border-radius: 12px; padding: 10px 12px; }
         .forecast-station strong { font-size: .8rem; }
@@ -181,7 +191,7 @@
             </div>
         </div>
         <div class="header-actions">
-            <div class="live-pill"><span class="live-dot"></span> LIVE DATA</div>
+            <div class="live-pill" id="live-pill"><span class="live-dot"></span> <span id="live-pill-text">LIVE DATA</span></div>
             <button id="replay-2024" type="button">▶ Replay Oct 2024 flood</button>
             <button id="refresh-button" type="button">↻ Refresh</button>
         </div>
@@ -211,6 +221,7 @@
             </div>
             <div class="loading-panel" id="loading"><div class="loading-card">Loading river conditions…</div></div>
             <div class="error-panel" id="error"><div><strong>Map data could not be loaded.</strong><br><span id="error-message"></span></div></div>
+            <div class="replay-clock" id="replay-clock"><strong id="replay-clock-time">—</strong><span id="replay-clock-sub"></span></div>
         </article>
 
         <aside class="side-card">
@@ -346,15 +357,23 @@
         return 'flow-surge';
     }
 
-    function renderRiverNetwork(riverNetwork, stations, readings) {
-        if (!riverNetwork) return;
-        const gauges = stations
+    function riverGauges(stations, readings) {
+        return stations
             .filter((s) => Number.isFinite(s.latitude) && Number.isFinite(s.longitude))
             .map((s) => ({ lat: s.latitude, lon: s.longitude, q: readings.get(s.station_code)?.discharge }))
             .filter((g) => g.q != null)
             .map((g) => ({ lat: g.lat, lon: g.lon, q: Number(g.q) }));
-        const flowBySegment = new Map();
-        (riverNetwork.features || []).forEach((f) => flowBySegment.set(f, nearestGaugeFlow(f, gauges)));
+    }
+
+    function segmentFlows(riverNetwork, gauges) {
+        const flows = new Map();
+        (riverNetwork.features || []).forEach((f) => flows.set(f, nearestGaugeFlow(f, gauges)));
+        return flows;
+    }
+
+    function renderRiverNetwork(riverNetwork, stations, readings) {
+        if (!riverNetwork) return;
+        const flowBySegment = segmentFlows(riverNetwork, riverGauges(stations, readings));
         const casing = L.geoJSON(riverNetwork, {
             style: (f) => ({ color: '#e3f4f8', weight: riverWeight(flowBySegment.get(f)) + 4.5, opacity: .8, lineCap: 'round' })
         }).addTo(state.map);
@@ -371,6 +390,41 @@
         flow.bringToBack();
         casing.bringToBack();
         state.layers.push(casing, flow);
+        state.riverNet = riverNetwork;
+        state.riverStations = stations;
+        state.riverCasing = casing;
+        state.riverFlow = flow;
+    }
+
+    // Restyle the existing river layers for a different set of readings (used by
+    // the replay). Colors and widths update; dash-speed classes stay as rendered.
+    function restyleRiver(readings) {
+        if (!state.riverFlow || !state.riverNet) return;
+        const flows = segmentFlows(state.riverNet, riverGauges(state.riverStations, readings));
+        state.riverCasing.setStyle((f) => ({ color: '#e3f4f8', weight: riverWeight(flows.get(f)) + 4.5, opacity: .8 }));
+        state.riverFlow.setStyle((f) => {
+            const q = flows.get(f);
+            return { color: q == null ? '#69b7d0' : flowColor(q), weight: riverWeight(q), opacity: .92 };
+        });
+    }
+
+    function updateStationMarker(code, discharge) {
+        const marker = state.markers.get(code);
+        if (!marker) return;
+        const q = discharge == null ? null : Number(discharge);
+        const color = flowColor(q);
+        const size = markerSize(q);
+        marker.setIcon(L.divIcon({
+            className: 'marker-wrap',
+            html: `<div class="flow-marker" style="--marker-color:${color};--marker-size:${size}px">${escapeHtml(code.replace('P.', ''))}</div>`,
+            iconSize: [size, size], iconAnchor: [size / 2, size / 2], popupAnchor: [0, -size / 2]
+        }));
+    }
+
+    function setLiveIndicator(mode, label) {
+        const pill = $('live-pill');
+        $('live-pill-text').textContent = label || 'LIVE DATA';
+        pill.classList.toggle('demo', mode !== 'live');
     }
 
     function renderMap(stations, readings, riverNetwork) {
@@ -733,55 +787,54 @@
         return `<div class="popup"><div class="popup-code">Marker</div><h3>${escapeHtml(poi.name)}</h3>${poi.note ? `<div class="popup-th">${escapeHtml(poi.note)}</div>` : ''}${riskHtml}</div>`;
     }
 
+    function endReplay() {
+        if (state.replayTimer) window.clearInterval(state.replayTimer);
+        state.replayTimer = null;
+        $('replay-2024').textContent = '▶ Replay Oct 2024 flood';
+        $('replay-clock').style.display = 'none';
+        setLiveIndicator('live');
+        loadDashboard();                                // restore live markers, river, zones
+    }
+
     async function replayFlood2024() {
         const button = $('replay-2024');
-        if (state.replayTimer) {                       // stop a running replay
-            window.clearInterval(state.replayTimer);
-            state.replayTimer = null;
-            state.p1Now = state.p1RealNow;
-            restyleFloodZones();
-            button.textContent = '▶ Replay Oct 2024 flood';
-            $('p1-peak').textContent = state.p1PeakText || '';
-            return;
-        }
+        if (state.replayTimer) { endReplay(); return; }
         button.textContent = 'Loading 2024 data…';
         try {
-            // pre-extracted static snapshot (15 kB); fall back to the live history API
-            let frames;
-            const staticResponse = await fetch('/static/flood-2024-p1.json');
-            if (staticResponse.ok) {
-                frames = await staticResponse.json();
-            } else {
-                const response = await fetch('/measurements/history/P.1?hours=876000&limit=100000');
-                if (!response.ok) throw new Error(`HTTP ${response.status}`);
-                const rows = await response.json();
-                frames = rows.filter((row) => {
-                    const t = row.timestamp;
-                    return t >= '2024-09-15' && t <= '2024-10-12' && row.water_level != null;
-                });
-            }
-            if (frames.length < 10) throw new Error('no 2024 data in history');
-            state.p1RealNow = state.p1Now;
-            state.p1PeakText = $('p1-peak').textContent;
+            const response = await fetch('/static/flood-2024-all.json');
+            if (!response.ok) throw new Error(`HTTP ${response.status}`);
+            const data = await response.json();
+            const n = data.timestamps.length;
+            if (n < 10) throw new Error('snapshot empty');
             state.zonesUserHidden = false;
             await showFloodZones(false);
             button.textContent = '⏹ Stop replay';
+            setLiveIndicator('replay', '⏪ 2024 REPLAY');
+            $('replay-clock').style.display = 'block';
             let i = 0;
             state.replayTimer = window.setInterval(() => {
-                const frame = frames[Math.min(i, frames.length - 1)];
-                state.p1Now = Number(frame.water_level);
-                const when = new Date(frame.timestamp).toLocaleString([], { day: 'numeric', month: 'short', hour: '2-digit' });
-                $('p1-peak').textContent = `⏪ 2024 flood replay · ${when} · P.1 at ${state.p1Now.toFixed(2)} m`;
+                const frame = Math.min(i, n - 1);
+                const readings = new Map();
+                let totalFlow = 0;
+                Object.entries(data.stations).forEach(([code, series]) => {
+                    const level = series.level[frame];
+                    const discharge = series.discharge[frame];
+                    readings.set(code, { water_level: level, discharge });
+                    updateStationMarker(code, discharge);
+                    if (discharge != null) totalFlow += discharge;
+                });
+                restyleRiver(readings);
+                const p1Level = data.stations['P.1'] ? data.stations['P.1'].level[frame] : null;
+                if (p1Level != null) state.p1Now = Number(p1Level);
                 restyleFloodZones();
-                i += 1;                                 // 1 h per frame (~45 s total)
-                if (i >= frames.length + 25) {          // hold the last frame briefly
-                    window.clearInterval(state.replayTimer);
-                    state.replayTimer = null;
-                    state.p1Now = state.p1RealNow;
-                    restyleFloodZones();
-                    button.textContent = '▶ Replay Oct 2024 flood';
-                    $('p1-peak').textContent = state.p1PeakText || '';
-                }
+                const ts = new Date(data.timestamps[frame]);
+                const when = ts.toLocaleString([], { day: 'numeric', month: 'short', hour: '2-digit' });
+                const p1Text = state.p1Now == null ? '—' : state.p1Now.toFixed(2) + ' m';
+                $('p1-peak').textContent = `⏪ 2024 flood replay · ${when} · P.1 at ${p1Text} · basin flow ${Math.round(totalFlow).toLocaleString()} m³/s`;
+                $('replay-clock-time').textContent = ts.toLocaleString([], { day: 'numeric', month: 'short', year: 'numeric', hour: '2-digit', minute: '2-digit' });
+                $('replay-clock-sub').textContent = `P.1 ${p1Text} · basin flow ${Math.round(totalFlow).toLocaleString()} m³/s`;
+                i += 2;                                 // 2 h per frame (~40 s total)
+                if (i >= n + 40) endReplay();           // hold the last frame briefly
             }, 120);
         } catch (error) {
             button.textContent = `Replay unavailable: ${error.message}`;
@@ -835,6 +888,7 @@
         const demoLevel = Number(params.get('demo_level'));
         const simulated = Number.isFinite(demoLevel) && demoLevel > 0;
         if (simulated) state.p1Now = demoLevel;
+        if ((simulated || params.has('demo_rise')) && !state.replayTimer) setLiveIndicator('sim', '⚠ SIMULATION');
         if (params.has('demo_rise') && !state.demoRiseTimer) {
             let level = state.p1Now ?? 2.2;
             state.demoRiseTimer = window.setInterval(() => {