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>

eslint.config.mjs

@@ -0,0 +1,77 @@
+import js from '@eslint/js';
+import typescript from '@typescript-eslint/eslint-plugin';
+import typescriptParser from '@typescript-eslint/parser';
+import globals from 'globals';
+
+export default [
+  {
+    ignores: ['node_modules/', 'dist/', 'public/*.css', '*.db', '*.scss', '*.md']
+  },
+  js.configs.recommended,
+  {
+    files: ['**/*.ts'],
+    languageOptions: {
+      parser: typescriptParser,
+      parserOptions: {
+        ecmaVersion: 2020,
+        sourceType: 'module'
+      },
+      globals: {
+        ...globals.node
+      }
+    },
+    plugins: {
+      '@typescript-eslint': typescript
+    },
+    rules: {
+      // TypeScript rules
+      '@typescript-eslint/no-unused-vars': 'error',
+      '@typescript-eslint/no-explicit-any': 'warn',
+      
+      // General rules
+      'no-console': 'off', // Allow console.log for server logging
+      'no-var': 'error',
+      'prefer-const': 'error',
+      'eqeqeq': 'error',
+      'no-unused-vars': 'off', // Use TypeScript version instead
+      
+      // Style rules
+      'indent': ['error', 2],
+      'quotes': ['error', 'single'],
+      'semi': ['error', 'always'],
+      'comma-dangle': ['error', 'never'],
+      'no-trailing-spaces': 'error'
+    }
+  },
+  {
+    files: ['**/*.js'],
+    languageOptions: {
+      globals: {
+        ...globals.node
+      }
+    },
+    rules: {
+      'no-console': 'off',
+      'no-var': 'error',
+      'prefer-const': 'error',
+      'eqeqeq': 'error',
+      'indent': ['error', 2],
+      'quotes': ['error', 'single'],
+      'semi': ['error', 'always'],
+      'comma-dangle': ['error', 'never'],
+      'no-trailing-spaces': 'error'
+    }
+  },
+  {
+    files: ['tests/**/*.ts'],
+    languageOptions: {
+      globals: {
+        ...globals.node,
+        ...globals.jest
+      }
+    },
+    rules: {
+      '@typescript-eslint/no-explicit-any': 'off' // Allow any in tests for mocks
+    }
+  }
+];