Add multi-day entries and area stay blocks

Entries gain an optional inclusive end_date (backfilled via migration): flights and travel longer than 24h show a continuation marker on following days, and a new stay entry type marks a time frame in one area (e.g. 3 days Venice) rendered as continuous bands across the calendar weeks. Stays feed the map route as stops; the route summary gains stays count and a chronological areas list with day spans. 49 API tests.

src/server/db.js

@@ -30,6 +30,7 @@ CREATE TABLE IF NOT EXISTS entries (
   id INTEGER PRIMARY KEY,
   trip_id INTEGER NOT NULL REFERENCES trips(id),
   date TEXT NOT NULL,
+  end_date TEXT,
   type TEXT NOT NULL,
   title TEXT NOT NULL,
   details TEXT DEFAULT '',
@@ -68,6 +69,7 @@ const MIGRATIONS = [
   { table: 'entries', column: 'split_mode', ddl: "ALTER TABLE entries ADD COLUMN split_mode TEXT NOT NULL DEFAULT 'equal'" },
   { 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' },
 ];
 
 function applyMigrations(db) {