ci(github): add linting and improve CI workflow

- Add ESLint configuration for backend TypeScript code
- Include linting step in backend quality checks
- Add linting step to GitHub Actions CI workflow
- Enable configurable Prisma query logging via PRISMA_LOG_QUERIES environment variable
- Update PrismaService to support dynamic log levels based on PRISMA_LOG_QUERIES
- Replace BadRequestException with UnauthorizedException in receipt import security tests

backend/package.json

@@ -11,8 +11,9 @@
     "prisma:migrate": "prisma migrate dev",
     "prisma:deploy": "prisma migrate deploy",
     "typecheck": "tsc --noEmit",
+    "lint": "eslint \"src/**/*.ts\"",
     "audit:high": "npm audit --audit-level=high",
-    "quality:ci": "npm run prisma:validate && npm run prisma:generate && npm run typecheck && npm test && npm run build && npm run audit:high",
+    "quality:ci": "npm run prisma:validate && npm run prisma:generate && npm run typecheck && npm run lint && npm test && npm run build && npm run audit:high",
     "test": "jest",
     "test:watch": "jest --watch"
   },
@@ -49,6 +50,9 @@
     "@types/passport-jwt": "^4.0.1",
     "@types/supertest": "^7.2.0",
     "@types/uuid": "^10.0.0",
+    "@typescript-eslint/eslint-plugin": "^8.46.2",
+    "@typescript-eslint/parser": "^8.46.2",
+    "eslint": "^9.38.0",
     "jest": "^29.7.0",
     "supertest": "^7.2.2",
     "ts-jest": "^29.2.6",