feat: comprehensive React SPA replacing Jinja2 UI

- New dark UI with 7 tabs: Rig, FX Chain, Models, IRs, Presets, Settings, Record
- All screens wired to live API endpoints
- Real-time state via WebSocket + polling fallback
- Models screen: list/load/unload/upload NAM files + Tone3000 search/install
- IRs screen: list/load/unload/upload IR files + Tone3000 search/install
- Presets screen: browse banks, activate, save, delete
- Settings screen: WiFi scan/connect/hotspot, Bluetooth/MIDI, 4CM routing
- Rig screen: live state, volume, bypass, tuner, signal chain
- FX Chain screen: block params, per-block bypass
- Serves at / instead of /ui
- Built with Vite, ~71KB gzipped

src/web/server.py

@@ -168,8 +168,15 @@ class WebServer:
         # ── HTML pages ──────────────────────────────────────────────
 
         @app.get("/", response_class=HTMLResponse)
-        async def dashboard(request: Request):
-            """Main dashboard — current preset, bypass, tuner, volume."""
+        async def root(request: Request):
+            """Serve the React SPA (or legacy dashboard as fallback)."""
+            # If we have a React build, serve it at /
+            if UI_DIST_DIR and UI_DIST_DIR.is_dir():
+                index_html = UI_DIST_DIR / "index.html"
+                if index_html.exists():
+                    content = index_html.read_text()
+                    return HTMLResponse(content)
+            # Fallback: legacy dashboard
             state = self._gather_state()
             ctx = {"request": request}
             ctx.update(state)