fix(sync): re-hydrate active trip store on reconnect/online (H1) (#1181)

setRefetchCallback was dead code, so on reconnect the queue flushed and Dexie
re-seeded but the open trip's Zustand store was never refreshed — a
collaborator's edits made while we were offline didn't appear until navigating
away and back.

- new tripStore.hydrateActiveTrip(): silent refresh of the active trip's
  collaborative state (days/places/packing/todo/budget/reservations/files),
  no resetTrip and no isLoading toggle so there's no splash on reconnect
- syncTriggers wires setRefetchCallback to it (WS layer awaits the flush hook
  first) and re-hydrates open trips after the online-event syncAll; cleared on
  unregister
- websocket exposes getActiveTrips() for the online-event path
- tests: refetch wiring + ordering, silent hydrate without reset/splash

client/tests/unit/tripStore.test.ts

@@ -259,6 +259,40 @@ describe('tripStore', () => {
     });
   });
 
+  describe('hydrateActiveTrip', () => {
+    const loadHandlers = (places: unknown[] = [], budget: unknown[] = []) => [
+      http.get('/api/trips/1', () => HttpResponse.json({ trip: buildTrip({ id: 1 }) })),
+      http.get('/api/trips/1/days', () => HttpResponse.json({ days: [] })),
+      http.get('/api/trips/1/places', () => HttpResponse.json({ places })),
+      http.get('/api/trips/1/packing', () => HttpResponse.json({ items: [] })),
+      http.get('/api/trips/1/todo', () => HttpResponse.json({ items: [] })),
+      http.get('/api/trips/1/budget', () => HttpResponse.json({ items: budget })),
+      http.get('/api/trips/1/reservations', () => HttpResponse.json({ reservations: [] })),
+      http.get('/api/trips/1/files', () => HttpResponse.json({ files: [] })),
+      http.get('/api/tags', () => HttpResponse.json({ tags: [] })),
+      http.get('/api/categories', () => HttpResponse.json({ categories: [] })),
+    ];
+
+    it('FE-TRIP-H1: silently refreshes resources without resetting or splashing', async () => {
+      server.use(...loadHandlers());
+      await useTripStore.getState().loadTrip(1);
+      expect(useTripStore.getState().trip!.id).toBe(1);
+
+      // New collaborative state arrives (as if edited by someone while we were offline).
+      const place = buildPlace({ trip_id: 1 });
+      const budgetItem = buildBudgetItem({ trip_id: 1 });
+      server.use(...loadHandlers([place], [budgetItem]));
+
+      await useTripStore.getState().hydrateActiveTrip(1);
+      const state = useTripStore.getState();
+
+      expect(state.places).toEqual([place]);
+      expect(state.budgetItems).toEqual([budgetItem]);
+      expect(state.trip!.id).toBe(1);      // trip not reset
+      expect(state.isLoading).toBe(false); // no splash toggled
+    });
+  });
+
   describe('refreshDays', () => {
     it('FE-TRIP-007: refreshDays re-fetches days and rebuilds assignments/dayNotes maps', async () => {
       const assignment = buildAssignment({ day_id: 20, order_index: 0 });