feat: hourly pricing + category base prices in booking modal + availability grid

- Add hourly_price column to rate_overrides, base_price/allow_hourly/hourly_base_price to room_categories (migration 033)
- Update categories and rate-overrides backend routes to handle new fields
- AvailabilityPage: hourly/nightly mode toggle, period prices auto-applied to grid with 'П' indicator, confirmation dialog when overriding period prices
- BookingModal: nightly/hourly toggle at top, pricing hierarchy (override → category base → room rate)
- RoomCategoriesPage: base_price/allow_hourly/hourly_base_price fields in category form; inline rooms panel
- CalendarPage + BookingCalendar: pass hourlyPriceOverrides and categoryBasePrices down to BookingModal

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

backend/migrations/033_category_pricing.sql

@@ -0,0 +1,9 @@
+-- Category pricing fields
+ALTER TABLE room_categories
+  ADD COLUMN IF NOT EXISTS base_price        INTEGER NOT NULL DEFAULT 0,
+  ADD COLUMN IF NOT EXISTS allow_hourly      BOOLEAN NOT NULL DEFAULT false,
+  ADD COLUMN IF NOT EXISTS hourly_base_price INTEGER NOT NULL DEFAULT 0;
+
+-- Hourly price override per date in availability grid
+ALTER TABLE rate_overrides
+  ADD COLUMN IF NOT EXISTS hourly_price INTEGER;