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/fuel-logs/domain/fuel-logs.service.ts

@@ -13,7 +13,7 @@ import {
 } from './fuel-logs.types';
 import { logger } from '../../../core/logging/logger';
 import { cacheService } from '../../../core/config/redis';
-import { pool } from '../../../core/config/database';
+import pool from '../../../core/config/database';
 
 export class FuelLogsService {
   private readonly cachePrefix = 'fuel-logs';

backend/src/features/vehicles/api/vehicles.controller.ts

@@ -6,7 +6,7 @@
 import { Request, Response, NextFunction } from 'express';
 import { VehiclesService } from '../domain/vehicles.service';
 import { VehiclesRepository } from '../data/vehicles.repository';
-import { pool } from '../../../core/config/database';
+import pool from '../../../core/config/database';
 import { logger } from '../../../core/logging/logger';
 import { ZodError } from 'zod';
 import {

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';