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

src/server/db.js

@@ -45,6 +45,7 @@ CREATE TABLE IF NOT EXISTS entries (
   split_mode TEXT NOT NULL DEFAULT 'equal',
   segments TEXT,
   rental TEXT,
+  transport_mode TEXT,
   created_at TEXT DEFAULT current_timestamp
 );
 
@@ -70,6 +71,7 @@ const MIGRATIONS = [
   { table: 'entries', column: 'segments', ddl: 'ALTER TABLE entries ADD COLUMN segments TEXT' },
   { table: 'entries', column: 'rental', ddl: 'ALTER TABLE entries ADD COLUMN rental TEXT' },
   { table: 'entries', column: 'end_date', ddl: 'ALTER TABLE entries ADD COLUMN end_date TEXT' },
+  { table: 'entries', column: 'transport_mode', ddl: 'ALTER TABLE entries ADD COLUMN transport_mode TEXT' },
 ];
 
 function applyMigrations(db) {
@@ -79,6 +81,15 @@ function applyMigrations(db) {
   }
 }
 
+// Data migrations for the 2026-07 entry-type rework (hotel/travel/immigration
+// removed in favour of stay/transport/activity). Naturally idempotent: after
+// the first run no rows of the legacy types remain, so re-running is a no-op.
+export function applyDataMigrations(db) {
+  db.exec("UPDATE entries SET type = 'stay' WHERE type = 'hotel'");
+  db.exec("UPDATE entries SET type = 'transport' WHERE type = 'travel'");
+  db.exec("UPDATE entries SET type = 'activity', title = '🛂 ' || title WHERE type = 'immigration'");
+}
+
 // Open (or create) the SQLite database at dbPath and ensure the schema exists.
 export function openDb(dbPath) {
   const db = new Database(dbPath);
@@ -86,5 +97,6 @@ export function openDb(dbPath) {
   db.pragma('foreign_keys = ON');
   db.exec(SCHEMA);
   applyMigrations(db);
+  applyDataMigrations(db);
   return db;
 }