Add real-time booking collaboration via WebSocket

- Backend: /ws relay endpoint (@fastify/websocket)
- Frontend: useHotelSocket hook with lock/unlock/booking events
- Calendar: lock overlay with diagonal stripes shows other manager editing

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

src/hooks/useHotelSocket.ts

@@ -0,0 +1,44 @@
+import { useEffect, useRef, useCallback } from 'react'
+import type { Booking } from '../types'
+
+export type WsMessage =
+  | { type: 'lock';            roomId: string; checkIn: string; checkOut: string; lockedBy: string }
+  | { type: 'unlock';          roomId: string }
+  | { type: 'booking:created'; booking: Booking }
+  | { type: 'booking:updated'; booking: Booking }
+  | { type: 'booking:deleted'; bookingId: string }
+
+interface Options {
+  slug: string
+  token: string | null
+  onMessage: (msg: WsMessage) => void
+}
+
+export function useHotelSocket({ slug, token, onMessage }: Options) {
+  const wsRef = useRef<WebSocket | null>(null)
+  const cbRef = useRef(onMessage)
+  cbRef.current = onMessage
+
+  useEffect(() => {
+    if (!slug || !token) return
+
+    const base = (import.meta.env.VITE_API_URL as string | undefined) ?? 'https://api.hotelsync.ru'
+    const wsBase = base.replace(/^https/, 'wss').replace(/^http(?!s)/, 'ws')
+    const ws = new WebSocket(`${wsBase}/ws?hotel=${encodeURIComponent(slug)}&token=${encodeURIComponent(token)}`)
+    wsRef.current = ws
+
+    ws.onmessage = (e) => {
+      try { cbRef.current(JSON.parse(e.data as string) as WsMessage) } catch { /* ignore */ }
+    }
+    ws.onerror = () => { /* silent */ }
+
+    return () => { ws.close(); wsRef.current = null }
+  }, [slug, token])
+
+  const send = useCallback((msg: WsMessage) => {
+    const ws = wsRef.current
+    if (ws?.readyState === WebSocket.OPEN) ws.send(JSON.stringify(msg))
+  }, [])
+
+  return { send }
+}