docs: describe React dashboard migration state

docs/data-flow.md

@@ -670,7 +670,32 @@ How the bot automatically replies to chat messages.
 
 ## Dashboard Data Flow
 
-How data flows from services to the web dashboard.
+How data flows from services to the React operator console.
+
+### Current React model
+
+1. Feature-local API clients request authoritative snapshots from `/api/*`.
+2. Shared Zod schemas in `packages/api-contracts` validate HTTP responses and
+   realtime envelopes at runtime.
+3. TanStack Query caches snapshots, preserves them during background refresh,
+   and owns mutation pending/error/success state.
+4. Operations opens `/api/events/stream`. Each typed event invalidates the
+   affected query keys, such as stats, timers, conversations, media, or
+   operations activity.
+5. Browser `EventSource` reconnects automatically. The client marks cached
+   state stale while reconnecting instead of blanking the UI.
+
+```text
+services/repositories -> Express /api snapshots -> Zod -> TanStack Query -> React routes
+          |                                                    ^
+          +-> realtime event hub -> /api/events/stream --------+
+```
+
+### Legacy fallback model
+
+The diagram below describes `public/index.html`, which remains only as a
+compatibility fallback until Express is switched to authenticated React static
+hosting and private-media protection is verified.
 
 ```
 ┌─────────────────────────────────────────────────────────────────┐
@@ -698,7 +723,7 @@ How data flows from services to the web dashboard.
 │     ├─► Update in-memory config                                │
 │     └─► Return updated config                                  │
 │                                                                 │
-│  ──── SSE LOG STREAMING ──────────────────────────────────────  │
+│  ──── LEGACY SSE LOG STREAMING ───────────────────────────────  │
 │                                                                 │
 │  GET /api/logs/stream                                          │
 │     ├─► Client connects                                        │
@@ -709,7 +734,7 @@ How data flows from services to the web dashboard.
 │     │   └─► Data: { level, message, timestamp }                │
 │     └─► On disconnect: unsubscribe                             │
 │                                                                 │
-│  ──── FRONTEND (public/index.html) ───────────────────────────  │
+│  ──── LEGACY FALLBACK (public/index.html) ────────────────────  │
 │                                                                 │
 │  JavaScript polls API endpoints:                               │
 │     ├─► /api/stats every 5 seconds                             │