Add comprehensive mobile-first responsive styles across billing, code-editor, file-upload, and main style sheets. Introduce a dedicated mobile.css file (702 lines) with hamburger navigation, sidebar overlay, pull-to-refresh indicator, and touch-friendly sizing. Integrate GestureHandler and PullToRefreshIndicator classes into file-list, file-preview, and file-upload-view components for swipe-to-close and pull-to-refresh interactions. Remove legacy inline media queries from style.css and link mobile.css in index.html.
- Implement two-factor authentication with TOTP verification, recovery codes, and QR code setup in auth flow
- Add is_starred and last_accessed_at fields to File and Folder models for bookmarking and recency tracking
- Introduce batch operation endpoints for files and folders (delete, star, unstar, move, copy)
- Configure structured logging with timestamps and module names, replacing print statements
- Register admin and starred routers, add global HTTPException handler with JSON error responses
- Update authenticate_user and create_access_token to handle 2FA verification and token claims
