feat: maintenance/blocked date ranges with booking overlap warning

- DB migration 020: add maintenance_from, maintenance_to to rooms
- Room type + RoomPayload: maintenanceFrom, maintenanceTo fields
- Context menu: clicking "На ремонт"/"Закрыт" expands inline date picker
  (С / По + "Без срока" checkbox), confirms with "Применить" button
- Calendar: stripe overlay covers only the maintenance date range
  (full row if no dates set, partial if date range specified)
- Booking creation: if drag-selected dates overlap with maintenance period,
  shows warning dialog with "Отмена" / "Всё равно забронировать"

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

src/lib/api.ts

@@ -442,6 +442,7 @@ export interface RoomPayload {
   extraPlace?: unknown; childPolicy?: unknown
   description?: string; photos?: string[]
   earlyCheckinFee?: number | null; lateCheckoutFee?: number | null
+  maintenanceFrom?: string | null; maintenanceTo?: string | null
 }
 
 function toRoomPayload(r: Partial<RoomPayload>): Record<string, unknown> {
@@ -467,6 +468,8 @@ function toRoomPayload(r: Partial<RoomPayload>): Record<string, unknown> {
   if (r.photos            !== undefined) out.photos               = r.photos
   if (r.earlyCheckinFee   !== undefined) out.early_checkin_fee    = r.earlyCheckinFee
   if (r.lateCheckoutFee   !== undefined) out.late_checkout_fee    = r.lateCheckoutFee
+  if (r.maintenanceFrom   !== undefined) out.maintenance_from     = r.maintenanceFrom
+  if (r.maintenanceTo     !== undefined) out.maintenance_to       = r.maintenanceTo
   return out
 }