Features:
- User registration and login with JWT tokens
- All data is now user-specific (multi-tenancy)
- Profile page with integrations and logout
- Automatic migration of existing data to first user
Backend changes:
- Added users and refresh_tokens tables
- Added user_id to all data tables (projects, entries, nodes, dictionaries, words, progress, configs, telegram_integrations, weekly_goals)
- JWT authentication middleware
- claimOrphanedData() for data migration
Frontend changes:
- AuthContext for state management
- Login/Register forms
- Profile page (replaced Integrations)
- All API calls use authFetch with Bearer token
Migration notes:
- On first deploy, backend automatically adds user_id columns
- First user to login claims all existing data
