feat: implement role-based access control for miniapp

- Introduced a new roles table in the database to manage user roles ('user' and 'admin') for access control.
- Updated the user model to include a foreign key reference to the roles table, allowing for role assignment.
- Enhanced command handlers to support the `/set_role` command for admins to assign roles to users.
- Refactored access control logic to utilize role checks instead of username/phone allowlists, improving security and maintainability.
- Updated documentation to reflect changes in access control mechanisms and role management.
- Added unit tests to ensure correct functionality of role assignment and access checks.

tests/test_handlers_init.py

@@ -9,5 +9,5 @@ def test_register_handlers_adds_all_handlers():
     """register_handlers: adds command, import, group pin handlers and error handler."""
     mock_app = MagicMock()
     register_handlers(mock_app)
-    assert mock_app.add_handler.call_count >= 9
+    assert mock_app.add_handler.call_count >= 10
     assert mock_app.add_error_handler.call_count == 1