fix(db): prevent migration-test database drop + correct AEG-X-004 evidence

Tests now guard against accidental drop of kartsell_migration_test by throwing
when the credential source DB is the destructive rehearsal target. Distinct
credential DB (kartselldb_test) prevents config collision.

AEG-X-004 evidence consolidated: rehearsal .trx files + preflight markdown
documented. Schema 0032 (shadow_run_queued_status_contract) verified
fresh/upgrade/recovery on isolated DB.

AGENTS.md: Necessity-driven (guard against destructive accident); no new feature.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

.gitignore

@@ -3,6 +3,7 @@
 frontend/node_modules/
 frontend/dist/
 frontend/.env.local
+frontend/test-results/
 .playwright/
 TestResults/
 *.user
@@ -13,3 +14,4 @@ __pycache__/
 *.log
 host*.log
 artifacts/
+publish-verify/