feat: connect RentalPage to API (objects + bookings persisted in DB)

- Add createObject/updateObject/deleteObject to api.rental
- Add RentalObjectPayload interface
- RentalPage now loads objects and bookings from API on mount
- Save/delete object operations call the API instead of only local state
- Save booking operations call the API (create or update)
- bufferMinutes from DB is now correctly passed to booking modal

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

src/lib/api.ts

@@ -317,6 +317,15 @@ export const api = {
     listObjects: (slug: string) =>
       req<RentalObjectApi[]>('GET', `/api/hotels/${slug}/rental-objects`),
 
+    createObject: (slug: string, data: RentalObjectPayload) =>
+      req<RentalObjectApi>('POST', `/api/hotels/${slug}/rental-objects`, data),
+
+    updateObject: (slug: string, id: string, data: Partial<RentalObjectPayload>) =>
+      req<RentalObjectApi>('PATCH', `/api/hotels/${slug}/rental-objects/${id}`, data),
+
+    deleteObject: (slug: string, id: string) =>
+      req<void>('DELETE', `/api/hotels/${slug}/rental-objects/${id}`),
+
     listBookings: (slug: string, from?: string, to?: string) => {
       const qs = new URLSearchParams()
       if (from) qs.set('from', from)
@@ -591,6 +600,20 @@ export interface RentalBookingPayload {
   notes?: string
 }
 
+export interface RentalObjectPayload {
+  name: string
+  icon?: string
+  color?: string
+  text_color?: string
+  price_per_hour?: number
+  price_per_day?: number
+  open_hour?: number
+  close_hour?: number
+  max_hours_per_slot?: number | null
+  buffer_minutes?: number
+  sort_order?: number
+}
+
 function toHotelPayload(h: HotelPayload): Record<string, unknown> {
   const out: Record<string, unknown> = {}
   if (h.name         !== undefined) out.name           = h.name