Add comprehensive backend features and mobile UI improvements

Backend:
- Add 2FA authentication with TOTP support
- Add API keys management system
- Add audit logging for security events
- Add file upload/management system
- Add notifications system with preferences
- Add session management
- Add webhooks integration
- Add analytics endpoints
- Add export functionality
- Add password policy enforcement
- Add new database migrations for core tables

Frontend:
- Add module position system (top/bottom sidebar sections)
- Add search and notifications module configuration tabs
- Add mobile logo replacing hamburger menu
- Center page title absolutely when no tabs present
- Align sidebar footer toggles with navigation items
- Add lighter icon color in dark theme for mobile
- Add API keys management page
- Add notifications page with context
- Add admin analytics and audit logs pages

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -2,5 +2,11 @@
 
 from app.models.user import User
 from app.models.settings import Settings
+from app.models.audit_log import AuditLog
+from app.models.api_key import APIKey
+from app.models.notification import Notification
+from app.models.session import UserSession
+from app.models.webhook import Webhook, WebhookDelivery
+from app.models.file import StoredFile
 
-__all__ = ["User", "Settings"]
+__all__ = ["User", "Settings", "AuditLog", "APIKey", "Notification", "UserSession", "Webhook", "WebhookDelivery", "StoredFile"]