- schema.sql: all user_id FKs now ON DELETE SET NULL (was RESTRICT)
- migrate_user_fk_set_null.py: drop+readd constraints on existing DBs
- entrypoint.sh: runs migration automatically on startup (non-fatal)
- db.py: rollback moved before FK check (cleanup)
Deleting a user now nullifies their references in audit_log,
project_context, context_files, change_requests, reviews instead of
blocking with a 409.
- entrypoint.sh: use NEEDS_INIT variable instead of exit codes (set -e was killing the script)
- __main__.py: skip db_path.exists() check when using PostgreSQL
- cli.py: use dual-backend placeholders for _seed_context (was using SQLite ? syntax)
- cli.py: use 'admin' instead of 'system' for seed updated_by (FK constraint)