feat: calendar hover price tooltip + AvailabilityPage API integration

- Calendar cells: hold mouse 600ms to show price tooltip for that date/room (baseRate + hourly rate if enabled)
- AvailabilityPage: load real categories from API, derive basePrice from room baseRates, fall back to room types if no categories
- Rate periods: persisted to DB via new /api/hotels/:slug/rate-periods endpoint
- New backend migration 021_rate_periods.sql + rate-periods route
- Added api.ratePeriods.{list,create,update,delete} to frontend API client

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

src/lib/api.ts

@@ -395,6 +395,21 @@ export const api = {
       req<void>('DELETE', `/api/hotels/${slug}/tariffs/${id}`),
   },
 
+  // ── Rate Periods ─────────────────────────────────────────────────────────
+  ratePeriods: {
+    list: (slug: string) =>
+      req<RatePeriodApi[]>('GET', `/api/hotels/${slug}/rate-periods`),
+
+    create: (slug: string, data: RatePeriodPayload) =>
+      req<RatePeriodApi>('POST', `/api/hotels/${slug}/rate-periods`, data),
+
+    update: (slug: string, id: string, data: Partial<RatePeriodPayload>) =>
+      req<RatePeriodApi>('PATCH', `/api/hotels/${slug}/rate-periods/${id}`, data),
+
+    delete: (slug: string, id: string) =>
+      req<void>('DELETE', `/api/hotels/${slug}/rate-periods/${id}`),
+  },
+
   // ── NetUP IPTV ────────────────────────────────────────────────────────────
   netup: {
     getSettings: (slug: string) =>
@@ -718,6 +733,31 @@ export interface TariffPayload {
   is_active?: boolean
 }
 
+export interface RatePeriodApi {
+  id: string
+  name: string
+  startDate: string
+  endDate: string
+  notes: string | null
+  categoryPrices: Record<string, number>
+  channelMarkup: Record<string, number>
+  extraPersonPrice: number
+  minNights: number
+  daysOfWeek: number[] | null
+}
+
+export interface RatePeriodPayload {
+  name: string
+  start_date: string
+  end_date: string
+  notes?: string
+  category_prices?: Record<string, number>
+  channel_markup?: Record<string, number>
+  extra_person_price?: number
+  min_nights?: number
+  days_of_week?: number[] | null
+}
+
 function toHotelPayload(h: HotelPayload): Record<string, unknown> {
   const out: Record<string, unknown> = {}
   if (h.name         !== undefined) out.name           = h.name