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

.gitea/workflows/deploy.yml

@@ -47,14 +47,6 @@ jobs:
           version: 11.1.3
           run_install: false
 
-      - name: Set up Rust
-        uses: dtolnay/rust-toolchain@stable
-        with:
-          targets: wasm32-unknown-unknown
-
-      - name: Install Trunk
-        run: cargo install trunk --version 0.22.0-beta.1 --locked
-
       - name: Install dependencies
         run: pnpm install --frozen-lockfile