fix: migrate E2E tests from SQLite to Postgres

- Rewrite e2e/seed.ts to use postgres driver instead of bun:sqlite
- Add userId to all seeded entities (multi-user schema)
- Add Postgres service container to CI E2E job
- Remove DATABASE_PATH from test server start script
- Re-enable E2E job in CI

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -228,6 +228,7 @@ uploads/*
 
 # Playwright
 e2e/test.db
+e2e/pgdata
 test-results/
 playwright-report/