Use Zod for schemas and add TypeScript linting with ESLint

AGENTS.md

@@ -35,3 +35,4 @@ This application uses Cloudflare Developer Platform, including Workers and Durab
 ## Implementation
 
 - When coding new features, create tests that cover the new code
+- Run code linting with `npm run lint` before commiting the code and fix the issues it highlights

eslint.config.mjs

@@ -0,0 +1,50 @@
+import eslint from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import globals from 'globals';
+
+export default [
+  eslint.configs.recommended,
+  ...tseslint.configs.recommended,
+  {
+    languageOptions: {
+      globals: {
+        ...globals.node,
+        ...globals.browser,
+      },
+    },
+  },
+  {
+    files: ['**/*.ts', '**/*.tsx'],
+    rules: {
+      '@typescript-eslint/no-explicit-any': 'off', // Too many existing instances to fix now
+      '@typescript-eslint/no-unused-vars': [
+        'warn',
+        {
+          argsIgnorePattern: '^_',
+          varsIgnorePattern: '^_',
+          caughtErrorsIgnorePattern: '^_',
+        },
+      ],
+      'no-empty': ['error', { allowEmptyCatch: true }],
+      'prefer-const': 'error',
+      'preserve-caught-error': 'off',
+      '@typescript-eslint/no-empty-object-type': 'off',
+    },
+  },
+  {
+    files: ['public/**/*.js'],
+    rules: {
+      'no-unused-vars': 'off', // Handled by typescript-eslint for ts files, but public js might need a different approach
+    },
+  },
+  {
+    ignores: [
+      'node_modules/',
+      '.wrangler/',
+      'dist/',
+      'coverage/',
+      'worker-configuration.d.ts',
+      'public/users/power-strip.js', // Existing legacy JS
+    ],
+  },
+];