- Add schema_version table; init_db detects a pre-M3/unknown DB (no version
row, or settings table missing the value column) and rebuilds to the clean
M3 schema, then stamps version 1
- _has_schema_version checks for a real row (empty table != versioned)
- _reset_for_tests checkpoints WAL before close (Windows handle release)
- TDD: test_schema_drift seeds the M2 settings shape, asserts rebuild + version
Fixes live 500 'no such column: value' on the UAT host (stale M2 slab_db volume).
Gates: check_requirements + check_coverage exit 0; pytest 14 passed.
Ty