Rework entry types: merge hotel into stay, transport with modes, auto-transport

- Type set is now activity/stay/transport/flight/rental/note; hotel, travel
  and immigration are removed with idempotent startup data migrations
  (hotel->stay, travel->transport, immigration->activity with flag prefix)
- Transport entries carry an optional mode (train/bus/ferry/taxi/drive/other)
  that drives the chip/map icon; route stops expose transport_mode
- Creating a stay auto-creates a bridging transport to its neighbouring
  stays unless a transport/flight already covers the gap (one-shot)
- Summary: transports count replaces hotels/travelLegs

tests/rental.test.js

@@ -68,7 +68,7 @@ test('rental: rejected on non-rental entries', async () => {
   const { agent } = await createAccount();
   const trip = await makeTrip(agent);
   const res = await agent.post(`/api/trips/${trip.id}/entries`).send({
-    date: '2026-08-01', type: 'hotel', title: 'Nope', rental: RENTAL,
+    date: '2026-08-01', type: 'activity', title: 'Nope', rental: RENTAL,
   });
   assert.equal(res.status, 400);
 });