Rental: connect to API, improve cell UI; remove price from room labels

Backend:
- Migration 015_rental.sql: rental_objects + rental_bookings tables, seed demo data
- New routes: GET/POST/PATCH/DELETE rental-objects and rental-bookings per hotel
- Register rentalRoutes in app.ts

Frontend:
- api.ts: add rental.listObjects, listBookings, createBooking, updateBooking, deleteBooking
- CalendarPage: fetch rental objects + bookings from API instead of mock data
- BookingCalendar: rental cell UI redesigned — colored squares + working hours + time slots (matches design spec)
- BookingCalendar: remove base rate price from desktop room label column (irrelevant with dynamic pricing)

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

backend/src/app.ts

@@ -19,6 +19,7 @@ import netupRoutes       from './routes/netup'
 import guestsRoutes        from './routes/guests'
 import bookingGuestsRoutes from './routes/booking-guests'
 import hotelSettingsRoutes from './routes/hotel-settings'
+import rentalRoutes        from './routes/rental'
 
 export async function buildApp() {
   const fastify = Fastify({
@@ -79,6 +80,7 @@ export async function buildApp() {
   await fastify.register(guestsRoutes)
   await fastify.register(bookingGuestsRoutes)
   await fastify.register(hotelSettingsRoutes)
+  await fastify.register(rentalRoutes)
 
   return fastify
 }