Fix: drag ghost visual, check-in date auto-fill, backend room_id patch

- BookingCalendar: replace tiny ghost badge with full-size booking block
  (same color, correct width based on nights × cell width, centered on cursor)
- BookingModal: auto-set check-out to check-in+1 day when check-in changes
- Backend PATCH /bookings/🆔 add room_id to allowed fields so drag-to-move saves correctly

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

src/components/bookings/BookingModal.tsx

@@ -1,5 +1,5 @@
 import { useState } from 'react'
-import { format } from 'date-fns'
+import { format, addDays } from 'date-fns'
 import { Star, Banknote, CreditCard, AlertCircle, Map, Plus, Trash2, Tag, Minus, BedDouble, Tv2, Send, Loader2, CheckCircle2 } from 'lucide-react'
 import { MOCK_DISCOUNTS } from '../../pages/DiscountsPage'
 import type { Discount } from '../../pages/DiscountsPage'
@@ -298,7 +298,13 @@ export function BookingModal({ open, draft, rooms, bookings = [], onClose, onSav
                     <input
                       type="date" className="input"
                       value={form.checkIn}
-                      onChange={e => set('checkIn', e.target.value)}
+                      onChange={e => {
+                        const newCheckIn = e.target.value
+                        set('checkIn', newCheckIn)
+                        if (newCheckIn && (!form.checkOut || form.checkOut <= newCheckIn)) {
+                          set('checkOut', format(addDays(new Date(newCheckIn), 1), 'yyyy-MM-dd'))
+                        }
+                      }}
                     />
                   </div>
                   <div>