Major UX improvements across multiple pages

Шахматка:
- Date/period picker dropdown on navigation button (choose start date + days window)
- Cancelled bookings fade out with animation after 1 second

Бронирования:
- Clickable column headers with sort asc/desc (Гость, Заезд, Выезд, Статус, Источник, Сумма)

Страница входа:
- Removed role-based account selector — just email + password
- System auto-detects role/hotel from credentials

Настройки:
- New "Бронирование" section with room assignment strategy (spread/together/sequential/manual)
- Notifications: SMTP email config + SMS provider config (SMSC, SMS.ru, МТС, etc.)

Модули:
- Added Housekeeping and Channel Manager as proper modules
- Channel Manager lists: Booking.com, Airbnb, Яндекс Путешествия, Островок, Суточно.ру, OneTwoTrip
- Housekeeping visible to all roles (including housekeeper) via module status
- Sidebar now uses module status to show/hide Уборка and Каналы

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

backend/src/db.ts

@@ -0,0 +1,8 @@
+import { Pool } from 'pg'
+import { config } from './config'
+
+export const db = new Pool({ connectionString: config.database.url })
+
+db.on('error', (err) => {
+  console.error('[DB] Unexpected client error:', err.message)
+})