feat: early check-in / late checkout fees with room-level configuration

- DB migration 016: add early_checkin_fee, late_checkout_fee to rooms table
- Backend rooms: support new fee columns in POST/PATCH
- Backend hotel-settings GET: also returns check_in_time, check_out_time
- Room type + RoomPayload: add earlyCheckinFee, lateCheckoutFee fields
- RoomModal: add fee amount inputs in pricing section
- SettingsPage: add toggles for early_checkin_enabled / late_checkout_enabled
- BookingDetailPanel: on check-in shows fee warning + adds payment record if
  current time is before checkInTime and fee is set on the room; same logic
  for check-out after checkOutTime

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/migrations/016_checkinout_fees.sql

@@ -0,0 +1,4 @@
+-- Add early check-in and late checkout fee fields to rooms
+ALTER TABLE rooms
+  ADD COLUMN IF NOT EXISTS early_checkin_fee DECIMAL(10,2) DEFAULT NULL,
+  ADD COLUMN IF NOT EXISTS late_checkout_fee DECIMAL(10,2) DEFAULT NULL;