Add client_tokens table with auto-generated sk-{hex} tokens so clients
created in the dashboard get working API keys. Auth flow: DB token lookup
first, then env token fallback, then permissive mode. Includes token
management CRUD endpoints and copy-once reveal modal in the frontend.
- Added 'users' table to database with bcrypt hashing.
- Refactored login to verify against the database.
- Implemented 'Security' section in settings to allow changing the admin password.
- Initialized system with default user 'admin' and password 'admin'.