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>

backend/app/schemas/room.py

@@ -49,3 +49,16 @@ class QueueAdd(BaseModel):
 
 class QueueAddMultiple(BaseModel):
     track_ids: list[UUID]
+
+
+class QueueItemResponse(BaseModel):
+    track: "TrackResponse"
+    added_by: UUID
+
+    class Config:
+        from_attributes = True
+
+
+# Import at the end to avoid circular imports
+from .track import TrackResponse
+QueueItemResponse.model_rebuild()