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>

tests/unit/services/DatabaseService.test.ts

@@ -5,7 +5,7 @@ describe('DatabaseService', () => {
 
   beforeEach(() => {
     databaseService = new DatabaseService();
-    
+
     // Mock console methods to reduce test noise
     jest.spyOn(console, 'log').mockImplementation(() => {});
     jest.spyOn(console, 'error').mockImplementation(() => {});
@@ -88,7 +88,7 @@ describe('DatabaseService', () => {
     it('should allow multiple instances', () => {
       const service1 = new DatabaseService();
       const service2 = new DatabaseService();
-      
+
       expect(service1).toBeInstanceOf(DatabaseService);
       expect(service2).toBeInstanceOf(DatabaseService);
       expect(service1).not.toBe(service2);