Fix TypeScript import inconsistencies causing GitHub Actions build failures

- Standardized pool imports to use default export consistently
- Changed from named import { pool } to default import pool
- Resolves "Cannot find module" errors in CI environment

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

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

backend/src/features/vehicles/tests/integration/vehicles.integration.test.ts

@@ -5,7 +5,7 @@
 
 import request from 'supertest';
 import { app } from '../../../../app';
-import { pool } from '../../../../core/config/database';
+import pool from '../../../../core/config/database';
 import { cacheService } from '../../../../core/config/redis';
 import { readFileSync } from 'fs';
 import { join } from 'path';