Fix ESLint issues in TypeScript codebase

- Add browser globals for frontend TypeScript files in ESLint config
- Fix unused parameter in MapImageService.generateErrorImage()
- Remove auto-fixable formatting issues (trailing spaces, indentation)

All ESLint errors now resolved, only warnings for 'any' types remain.

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

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

eslint.config.mjs

@@ -62,6 +62,41 @@ export default [
       'no-trailing-spaces': 'error'
     }
   },
+  {
+    files: ['src/frontend/**/*.ts'],
+    languageOptions: {
+      parser: typescriptParser,
+      parserOptions: {
+        ecmaVersion: 2020,
+        sourceType: 'module'
+      },
+      globals: {
+        ...globals.browser
+      }
+    },
+    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 debugging
+      '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: ['tests/**/*.ts'],
     languageOptions: {

src/server.ts

@@ -248,10 +248,10 @@ function setupRoutes(): void {
 
       const escapeHtml = (text: string): string => {
         return text.replace(/&/g, '&')
-                   .replace(/</g, '&lt;')
+          .replace(/</g, '&lt;')
-                   .replace(/>/g, '&gt;')
+          .replace(/>/g, '&gt;')
-                   .replace(/"/g, '&quot;')
+          .replace(/"/g, '&quot;')
-                   .replace(/'/g, '&#39;');
+          .replace(/'/g, '&#39;');
       };
 
       const tableRows = locations.map((location, index) => `

src/services/MapImageService.ts

@@ -29,7 +29,7 @@ export class MapImageService {
       return mapboxBuffer;
     } else {
       // Return a simple error image if Mapbox fails
-      return this.generateErrorImage(opts);
+      return this.generateErrorImage();
     }
   }
 
@@ -120,7 +120,7 @@ export class MapImageService {
   /**
    * Generate a simple error image when Mapbox fails
    */
-  private generateErrorImage(options: MapOptions): Buffer {
+  private generateErrorImage(): Buffer {
     // Generate a simple 1x1 transparent PNG as fallback
     // This is a valid PNG header + IHDR + IDAT + IEND for a 1x1 transparent pixel
     const transparentPng = Buffer.from([