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>

CLAUDE.md

@@ -58,9 +58,18 @@ npm run build-css:dev
 npm run watch-css
 ```
 
+### Code Quality
+```bash
+# Run ESLint to check code style and quality
+npm run lint
+
+# Auto-fix ESLint issues where possible
+npm run lint:fix
+```
+
 ### Testing
 ```bash
-# Run all tests (125+ tests with TypeScript)
+# Run all tests (128+ tests with TypeScript)
 npm test
 
 # Run tests with coverage report (76% overall coverage)