Add coordinate validation and ESLint integration

- Add explicit latitude/longitude validation in location submissions
- Implement ESLint with TypeScript support and flat config
- Auto-fix 621 formatting issues across codebase
- Add comprehensive tests for coordinate validation
- Update documentation with lint scripts and validation rules
- Maintain 128 passing tests with enhanced security

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

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

package.json

@@ -17,6 +17,8 @@
     "build:ts": "tsc",
     "test": "jest --runInBand --forceExit",
     "test:coverage": "jest --coverage",
+    "lint": "eslint src/ tests/",
+    "lint:fix": "eslint src/ tests/ --fix",
     "postinstall": "npm run build-css"
   },
   "dependencies": {
@@ -39,7 +41,11 @@
     "@types/supertest": "^6.0.3",
     "@types/swagger-jsdoc": "^6.0.4",
     "@types/swagger-ui-express": "^4.1.8",
+    "@typescript-eslint/eslint-plugin": "^8.35.1",
+    "@typescript-eslint/parser": "^8.35.1",
     "concurrently": "^9.2.0",
+    "eslint": "^9.30.1",
+    "globals": "^16.3.0",
     "jest": "^29.7.0",
     "jest-environment-node": "^30.0.4",
     "nodemon": "^3.1.10",