feat(dashboard): complete React cutover

docs/data-flow.md

@@ -691,11 +691,10 @@ services/repositories -> Express /api snapshots -> Zod -> TanStack Query -> Reac
           +-> realtime event hub -> /api/events/stream --------+
 ```
 
-### Legacy fallback model
+### Retired legacy 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.
+The historical diagram below is retained for migration context only.
+`public/index.html` has been removed and is no longer served.
 
 ```
 ┌─────────────────────────────────────────────────────────────────┐
@@ -734,7 +733,7 @@ hosting and private-media protection is verified.
 │     │   └─► Data: { level, message, timestamp }                │
 │     └─► On disconnect: unsubscribe                             │
 │                                                                 │
-│  ──── LEGACY FALLBACK (public/index.html) ────────────────────  │
+│  ──── RETIRED LEGACY IMPLEMENTATION ──────────────────────────  │
 │                                                                 │
 │  JavaScript polls API endpoints:                               │
 │     ├─► /api/stats every 5 seconds                             │