chore: add ESLint + Prettier frontend linting

.github/workflows/ci.yml

@@ -40,6 +40,9 @@ jobs:
       - name: Install npm dependencies
         run: npm ci
 
+      - name: Lint frontend
+        run: npm run lint
+
       - name: Build frontend
         run: npm run build
 

.prettierrc

@@ -0,0 +1,7 @@
+{
+  "semi": true,
+  "singleQuote": true,
+  "tabWidth": 2,
+  "trailingComma": "es5",
+  "printWidth": 100
+}

eslint.config.js

@@ -0,0 +1,71 @@
+import js from '@eslint/js';
+import globals from 'globals';
+import react from 'eslint-plugin-react';
+import reactHooks from 'eslint-plugin-react-hooks';
+import prettier from 'eslint-config-prettier';
+
+/**
+ * ESLint flat config for CLAI frontend.
+ *
+ * React 19 hooks rules are intentionally disabled for now because the
+ * existing codebase was written before these strict rules existed.
+ * Re-enable them incrementally in follow-up PRs:
+ *   - react-hooks/set-state-in-effect
+ *   - react-hooks/exhaustive-deps
+ *   - react-hooks/preserve-manual-memoization
+ *   - react-hooks/refs
+ *   - react-hooks/immutability
+ *   - react-hooks/use-memo
+ *   - react-hooks/purity
+ */
+export default [
+  js.configs.recommended,
+  {
+    files: ['**/*.{js,jsx}'],
+    languageOptions: {
+      ecmaVersion: 'latest',
+      sourceType: 'module',
+      globals: {
+        ...globals.browser,
+        ...globals.es2021,
+      },
+      parserOptions: {
+        ecmaFeatures: {
+          jsx: true,
+        },
+      },
+    },
+    plugins: {
+      react,
+      'react-hooks': reactHooks,
+    },
+    rules: {
+      ...react.configs.recommended.rules,
+      'react/react-in-jsx-scope': 'off',
+      'react/prop-types': 'off',
+      'react/display-name': 'off',
+      'react/no-unescaped-entities': 'off',
+      'no-unused-vars': ['warn', { argsIgnorePattern: '^_' }],
+      // Disabled React 19 strict hooks rules (see top comment)
+      'react-hooks/set-state-in-effect': 'off',
+      'react-hooks/exhaustive-deps': 'off',
+      'react-hooks/preserve-manual-memoization': 'off',
+      'react-hooks/refs': 'off',
+      'react-hooks/immutability': 'off',
+      'react-hooks/use-memo': 'off',
+      'react-hooks/purity': 'off',
+    },
+    settings: {
+      react: {
+        version: 'detect',
+      },
+    },
+  },
+  {
+    files: ['**/*.config.{js,mjs,cjs}'],
+    languageOptions: {
+      globals: globals.node,
+    },
+  },
+  prettier,
+];