feat: initial commit — local services (backend + manager dashboard + waiter PWA)

Includes all work to date:
- local_backend: FastAPI backend with products, orders, tables, shifts, cloud sync
- manager_dashboard: React manager UI with product/category management, reports, settings
- waiter_pwa: React PWA for waiter devices
- Category reparent endpoint and UI
- Waiter domain: local_ip sent on heartbeat, waiter_domain persisted from cloud response
- QR code modal in AppInfoTab for waiter domain
- Product form: number input spinners removed, category pre-selected on new product
- Category row: count badge moved to far right

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

waiter_pwa/src/hooks/useSSE.js

@@ -0,0 +1,93 @@
+import { useCallback, useEffect, useRef } from 'react'
+
+const INITIAL_RECONNECT_DELAY = 3000
+const MAX_RECONNECT_DELAY = 30000
+
+/**
+ * Opens an SSE connection to /api/sse/stream?token=<jwt>.
+ *
+ * Callbacks (onEvent, onConnect, onDisconnect) are stored in refs so they are
+ * always current without causing the EventSource to reconnect when they change.
+ *
+ * The connection is created/destroyed only when `token` or `enabled` changes.
+ */
+export function useSSE({ token, onEvent, onConnect, onDisconnect, enabled = true }) {
+  // Keep callbacks in refs so the EventSource closure always calls the latest version
+  const onEventRef = useRef(onEvent)
+  const onConnectRef = useRef(onConnect)
+  const onDisconnectRef = useRef(onDisconnect)
+  useEffect(() => { onEventRef.current = onEvent }, [onEvent])
+  useEffect(() => { onConnectRef.current = onConnect }, [onConnect])
+  useEffect(() => { onDisconnectRef.current = onDisconnect }, [onDisconnect])
+
+  const esRef = useRef(null)
+  const reconnectTimer = useRef(null)
+  const reconnectDelay = useRef(INITIAL_RECONNECT_DELAY)
+  const unmounted = useRef(false)
+  // Expose reconnect so SSEContext can trigger it after heartbeat recovery
+  const reconnectRef = useRef(null)
+
+  useEffect(() => {
+    if (!token || !enabled) return
+    unmounted.current = false
+
+    function connect() {
+      if (unmounted.current) return
+      if (esRef.current) {
+        esRef.current.close()
+        esRef.current = null
+      }
+
+      const url = `/api/sse/stream?token=${encodeURIComponent(token)}`
+      const es = new EventSource(url)
+      esRef.current = es
+
+      es.onopen = () => {
+        reconnectDelay.current = INITIAL_RECONNECT_DELAY
+        onConnectRef.current?.()
+      }
+
+      es.onmessage = (e) => {
+        try {
+          const { type, data } = JSON.parse(e.data)
+          onEventRef.current?.(type, data)
+        } catch {
+          // malformed event — ignore
+        }
+      }
+
+      es.onerror = () => {
+        es.close()
+        esRef.current = null
+        onDisconnectRef.current?.()
+        if (unmounted.current) return
+        reconnectTimer.current = setTimeout(() => {
+          reconnectDelay.current = Math.min(
+            reconnectDelay.current * 1.5,
+            MAX_RECONNECT_DELAY
+          )
+          connect()
+        }, reconnectDelay.current)
+      }
+    }
+
+    reconnectRef.current = connect
+    connect()
+
+    return () => {
+      unmounted.current = true
+      clearTimeout(reconnectTimer.current)
+      esRef.current?.close()
+      esRef.current = null
+    }
+  }, [token, enabled])
+
+  // Stable reference — never changes, so heartbeat useEffect dep array stays stable
+  const reconnect = useCallback(() => {
+    clearTimeout(reconnectTimer.current)
+    reconnectDelay.current = INITIAL_RECONNECT_DELAY
+    reconnectRef.current?.()
+  }, [])
+
+  return { reconnect }
+}