Add transport sync button and allow dropping stays onto band-covered days

- Auto-created transports carry auto_ref {from,to} stay ids; new
  POST /api/trips/:id/transports/regenerate reconciles them against the
  current stay order (re-date/re-title kept bridges preserving mode and
  price, delete orphans, create missing) without touching manual
  transports or flight-covered gaps
- Sync transports button in the calendar header with result toast
- The week band strip is now a drop target resolving the day from the
  pointer position, so stays can be dropped onto spots covered by other
  stays; overlapping stays stack in band lanes

src/server/routes/entries.js

@@ -4,6 +4,7 @@ import { membership } from '../util/access.js';
 import { ENTRY_COLUMNS, attachParticipants } from '../util/entrySerialize.js';
 import { validateSegments } from '../util/segments.js';
 import { validateRental } from '../util/rental.js';
+import { autoTransportTitle } from '../util/autoTransport.js';
 
 const ENTRY_TYPES = new Set(['flight', 'transport', 'activity', 'rental', 'stay', 'note']);
 const TRANSPORT_MODES = new Set(['train', 'bus', 'ferry', 'taxi', 'drive', 'other']);
@@ -234,8 +235,8 @@ export default function entriesRoutes(db) {
      AND date >= ? AND date <= ? LIMIT 1`
   );
   const insertAutoTransport = db.prepare(
-    `INSERT INTO entries (trip_id, date, type, title, details, sort_order, split_mode)
-     VALUES (?, ?, 'transport', ?, '', 0, 'equal')`
+    `INSERT INTO entries (trip_id, date, type, title, details, sort_order, split_mode, auto_ref)
+     VALUES (?, ?, 'transport', ?, '', 0, 'equal', ?)`
   );
 
   const memberIdSet = (tripId) => new Set(getMemberIds.all(tripId).map((r) => r.user_id));
@@ -247,12 +248,6 @@ export default function entriesRoutes(db) {
     }
   }
 
-  // Short name for an auto-transport title: first comma-segment of the stay's
-  // location_name, falling back to its title.
-  function shortName(stay) {
-    return (stay.location_name || stay.title).split(',')[0].trim();
-  }
-
   // Auto-create a transport entry bridging `earlier` -> `later` (both stay
   // rows) unless a transport/flight already covers the gap, or the window is
   // inverted (overlapping stays).
@@ -261,8 +256,12 @@ export default function entriesRoutes(db) {
     const windowEnd = later.date;
     if (windowStart > windowEnd) return;
     if (existsTransportOrFlightInWindow.get(tripId, windowStart, windowEnd)) return;
-    const title = `${shortName(earlier)} → ${shortName(later)}`;
-    insertAutoTransport.run(tripId, later.date, title);
+    insertAutoTransport.run(
+      tripId,
+      later.date,
+      autoTransportTitle(earlier, later),
+      JSON.stringify({ from: earlier.id, to: later.id })
+    );
   }
 
   // Fires once, on stay creation: bridges the new stay to its nearest