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/types/index.ts

@@ -101,6 +101,8 @@ export interface Room {
   childPolicy?: ChildPolicy
   earlyCheckinFee?: number
   lateCheckoutFee?: number
+  maintenanceFrom?: string | null  // ISO date, null = indefinite start
+  maintenanceTo?: string | null    // ISO date, null = indefinite end
 }
 
 export interface DocumentTemplate {