Add agent_config_revisions table for tracking agent configuration changes with
rollback support. Add issue_approvals junction table linking issues to approvals.
New migrations (0005, 0006) for permissions column and new tables. Rework migration
client with statement-level idempotency checks (table/column/index/constraint
existence) so migrations can be safely retried against partially-migrated databases.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
