Changes:
- Removed server_default with CURRENT_TIMESTAMP from User model (SQLite doesn't support non-constant defaults in ALTER TABLE)
- Updated migrations 002 and 003 to add datetime columns without server defaults
- Added manual timestamp updates using SQLite's datetime('now') function in migrations
- Modified User model to handle timestamps in Python code instead of database defaults
- Updated profile routes to manually set updated_at timestamps on profile changes
- Enhanced User model __init__ to set default timestamps for new users
This resolves the 'Cannot add a column with non-constant default' SQLite error
while maintaining proper timestamp functionality.
3e90deba20