fix: resolve TypeScript and linting errors in test infrastructure

- Add @types/better-sqlite3 dependency
- Remove duplicate database mock file
- Fix property spread order in workflow builder to prevent overwrites
- All 75 tests now pass with no linting errors

🤖 Generated with [Claude Code](https://claude.ai/code)

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

package.json

@@ -92,6 +92,7 @@
   "devDependencies": {
     "@faker-js/faker": "^9.9.0",
     "@testing-library/jest-dom": "^6.6.4",
+    "@types/better-sqlite3": "^7.6.13",
     "@types/express": "^5.0.3",
     "@types/node": "^22.15.30",
     "@types/ws": "^8.18.1",