Redesign UI with Vuetify and improve configuration

Major changes:
- Full UI redesign with Vuetify 3 (dark theme, modern components)
- Sidebar navigation with gradient logo
- Redesigned player controls with Material Design icons
- New room cards, track lists, and filter UI with chips
- Modern auth pages with centered cards

Configuration improvements:
- Centralized all settings in root .env file
- Removed redundant backend/.env and frontend/.env files
- Increased file upload limit to 100MB (nginx + backend)
- Added build args for Vite environment variables
- Frontend now uses relative paths (better for domain deployment)

UI Components updated:
- App.vue: v-navigation-drawer with sidebar
- MiniPlayer: v-footer with modern controls
- Queue: v-list with styled items
- RoomView: improved filters with clickable chips
- All views: Vuetify cards, buttons, text fields

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/main.js

@@ -2,11 +2,13 @@ import { createApp } from 'vue'
 import { createPinia } from 'pinia'
 import App from './App.vue'
 import router from './router'
+import vuetify from './plugins/vuetify'
 import './assets/styles/main.css'
 
 const app = createApp(App)
 
 app.use(createPinia())
 app.use(router)
+app.use(vuetify)
 
 app.mount('#app')