- Add _schema_migrations table to track applied migrations
- Each migration has a unique name and checksum
- Migrations are only run once (tracked by name)
- Checksum changes are detected and logged as warnings
- Smart error detection distinguishes "already applied" errors from real failures
- Real errors now fail hard with clear error messages
- Safe PostgreSQL error codes (42P07, 42701, 42710, 42P16) are recognized
- Fix semver migration to generate UUID for id column
When a migration fails, the transaction is left in a failed state. Without
rollback, all subsequent migrations fail with "current transaction is aborted".
This was preventing the team_id column from being added to projects.
