Previously, a single failed migration would abort all subsequent
migrations via raise RuntimeError. Now the runner logs the failure
and continues with remaining migrations, so independent schema
changes (e.g. 050-053) are not blocked by an unrelated failure
in an earlier migration (e.g. 048).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Adds migration_runner.py that executes pending migrations from
migrations/ directory when backend-compliance starts. Tracks applied
migrations in _migration_history table.
Handles existing databases: detects if tables from migrations 001-045
already exist and seeds the history table accordingly, so only new
migrations (046+) are applied.
Skippable via SKIP_MIGRATIONS=true env var.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>