feat: migrate Leptos frontend to Next.js 16 (React 19)

Complete migration from services/frontend.old/ (Leptos 0.7 WASM + Rust)
to services/frontend/ (Next.js 16 static export + TypeScript + Tailwind v4).

Summary:
- Port all shared types (message, guild, voice, media, dashboard, recording, ui)
- Build fetch-based API client covering all 30+ backend endpoints
- WebSocket client with auto-reconnect (exponential backoff, 20 attempts)
- React context provider for WS with typed event subscription (22 event types)
- Login page with localStorage auth + auto-redirect
- Dashboard layout with sidebar, header (WS status + theme toggle)
- Messages: feed, search, images tab, review tab, channel filter, detail modal
- Live: voice connection, music player, recordings, mic transmit, active speakers
- Dashboard: stats, user list, channel list, detail views
- Mascot chatbot with history + clear
- uiStateApi persistence for selected tab
- Add static export config, update deploy scripts and CI

package.json

@@ -7,9 +7,9 @@
   "scripts": {
     "dev:backend": "pnpm --filter './services/backend' run dev",
     "dev:discord-gateway": "pnpm --filter './services/discord-gateway' run dev",
-    "dev:web": "cd services/frontend/frontend && trunk serve --address 0.0.0.0",
-    "build:web": "cd services/frontend/frontend && trunk build --release",
-    "typecheck:web": "cd services/frontend/frontend && cargo check",
+    "dev:web": "pnpm --filter './services/frontend' run dev",
+    "build:web": "pnpm --filter './services/frontend' run build",
+    "typecheck:web": "cd services/frontend && bun run build",
     "build:backend": "pnpm --filter './services/backend' run build",
     "build:discord-gateway": "pnpm --filter './services/discord-gateway' run build",
     "typecheck": "pnpm -r run typecheck",