chore(test): add test infrastructure, CI config, and security scanning

- Add Jenkinsfile with E2E/visual regression/security scan stages
- Add Stryker mutation testing configuration
- Add security header scanning script (check-security-headers.ts)
- Remove old playwright.config.ts (migrated to e2e/playwright.config.ts)
- Remove obsolete .claude/skills/impeccable
- Update jest config for test path patterns
- Update package.json with comprehensive test scripts
- Update .gitignore for stryker-tmp/ and .pi/ temp files

.gitignore

@@ -266,6 +266,15 @@ performance-baseline.json
 test-data-*.json
 test-results-*.json
 
+# Stryker mutation testing temp files
+.stryker-tmp/
+
+# Pi framework temp files
+.pi/
+
+# Agent config (local only)
+.agents/settings.local.json
+
 # Additional E2E test artifacts
 e2e/blob-report/
 e2e/report/