feat: support check-in time ranges for hotel accommodations

- Add check_in_end column to day_accommodations (Migration 102)
- Server: create/update accommodation accepts check_in_end
- Bidirectional sync: check_in_end synced between accommodation
  and linked reservation metadata (check_in_end_time)
- DayDetailPanel: shows check-in range (e.g. "14:00 – 22:00"),
  new "Until" time picker in hotel form
- ReservationModal: new check-in-until field for hotel bookings
- ReservationsPanel: displays check-in range in metadata cells
- i18n: checkInUntil keys in all 15 languages

Closes #366

client/src/i18n/translations/de.ts

@@ -1015,6 +1015,7 @@ const de: Record<string, string | { name: string; category: string }[]> = {
   'reservations.meta.platform': 'Gleis',
   'reservations.meta.seat': 'Sitzplatz',
   'reservations.meta.checkIn': 'Check-in',
+  'reservations.meta.checkInUntil': 'Check-in bis',
   'reservations.meta.checkOut': 'Check-out',
   'reservations.meta.linkAccommodation': 'Unterkunft',
   'reservations.meta.pickAccommodation': 'Mit Unterkunft verknüpfen',
@@ -1499,6 +1500,7 @@ const de: Record<string, string | { name: string; category: string }[]> = {
   'day.noPlacesForHotel': 'Füge zuerst Orte zu deiner Reise hinzu',
   'day.allDays': 'Alle',
   'day.checkIn': 'Check-in',
+  'day.checkInUntil': 'Bis',
   'day.checkOut': 'Check-out',
   'day.confirmation': 'Bestätigung',
   'day.editAccommodation': 'Unterkunft bearbeiten',