fix: restore station telemetry and make river flow visualization data-driven

Station selection showed no history since 21ca844: Chart.js v4 datasets
had parsing:false with plain number arrays, drawing empty axes. Remove
the flag so the chart parses values again.

Backend hardening for the same flow:
- /measurements/history/{code} no longer 503s on non-Postgres configs;
  it falls back to the configured adapter (reversed to ascending order)
- DB_TYPE defaults to postgresql when POSTGRES_CONNECTION_STRING is set
  and DB_TYPE is unset, so the .env psql wins over the sqlite default
- zero readings (0.0) are no longer coerced to None, which would fail
  MeasurementResponse validation and 500 /measurements/latest

Map visualization:
- river segments are now colored, widened and dash-speed-animated by
  the discharge at the nearest gauge (same scale as the marker legend)
- fix z-order bug that drew the animated flow line behind its casing
- legend entries for river lines, reduced-motion fallback

River geometry: rebuild ping-river-network.geojson from Overpass
(110 -> 202 features), restoring missing Ping mainstem reaches through
the Bhumibol reservoir and the Tak-Kamphaeng Phet braided section
(unnamed waterway=river ways in OSM), with short synthetic connectors
(connector: true) bridging remaining sub-8 km holes.

src/web_api.py

@@ -454,7 +454,7 @@ async def get_postgres_history(
     hours: int = Query(168, ge=1),
     limit: int = Query(50000, ge=1, le=100000),
 ):
-    """Get historical measurements for a station from PostgreSQL."""
+    """Get historical measurements for a station from the configured database."""
     cache_key = f"{station_code}:{hours}:{limit}"
     now = time.monotonic()
     with HISTORY_CACHE_LOCK:
@@ -463,25 +463,36 @@ async def get_postgres_history(
             return cached[1]
     try:
         db_config = Config.get_database_config()
-        if db_config["type"] != "postgresql":
-            raise RuntimeError("PostgreSQL is not configured")
-        history = PostgresHistory(db_config["connection_string"])
         end_time = datetime.now()
-        data = await asyncio.to_thread(
-            history.station_history,
-            station_code,
-            end_time - timedelta(hours=hours),
-            end_time,
-            limit,
-        )
+        if db_config["type"] == "postgresql":
+            history = PostgresHistory(db_config["connection_string"])
+            data = await asyncio.to_thread(
+                history.station_history,
+                station_code,
+                end_time - timedelta(hours=hours),
+                end_time,
+                limit,
+            )
+        else:
+            scraper = app_state["scraper"]
+            if not scraper or not scraper.db_adapter:
+                raise RuntimeError("Database not available")
+            rows = await asyncio.to_thread(
+                scraper.db_adapter.get_measurements_by_timerange,
+                end_time - timedelta(hours=hours),
+                end_time,
+                [station_code],
+            )
+            # adapter returns newest-first; keep the newest `limit` rows, chart wants ascending
+            data = list(reversed(rows[:limit]))
         with HISTORY_CACHE_LOCK:
             HISTORY_CACHE[cache_key] = (now, data)
         return data
     except RuntimeError as error:
         raise HTTPException(status_code=503, detail=str(error))
     except Exception as error:
-        logger.error(f"Error fetching PostgreSQL history: {error}")
-        raise HTTPException(status_code=502, detail="PostgreSQL history unavailable")
+        logger.error(f"Error fetching measurement history: {error}")
+        raise HTTPException(status_code=502, detail="Measurement history unavailable")
 
 
 @app.get("/measurements/latest", response_model=List[MeasurementResponse])