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

frontend-react/vite.config.js

@@ -0,0 +1,12 @@
+import { defineConfig } from 'vite'
+import react from '@vitejs/plugin-react'
+
+// https://vite.dev/config/
+export default defineConfig({
+  plugins: [react()],
+  base: '/ui/',
+  build: {
+    outDir: '../src/web/ui-dist',
+    emptyOutDir: true,
+  },
+})