chore(eslint): migrate to ESLint 9 flat config format

- Add eslint.config.js with ESLint 9 flat config format
- Remove deprecated .eslintrc.cjs file
- Remove deprecated .eslintignore file (replaced by ignores in config)
- Maintain all existing ESLint rules and configurations
- Ensure compatibility with Husky 9.1.7

frontend/.eslintignore

@@ -1,17 +0,0 @@
-node_modules/
-dist/
-prettier.config.cjs
-.eslintrc.cjs
-env.d.ts
-public/
-assets/
-vite-env.d.ts
-.prettierignore
-package-lock.json
-package.json
-postcss.config.cjs
-prettier.config.cjs
-tailwind.config.cjs
-tsconfig.json
-tsconfig.node.json
-vite.config.ts

frontend/.eslintrc.cjs

@@ -1,48 +0,0 @@
-module.exports = {
-  env: {
-    browser: true,
-    es2021: true,
-    node: true,
-  },
-  extends: [
-    'eslint:recommended',
-    'plugin:@typescript-eslint/recommended',
-    'plugin:react/recommended',
-    'plugin:prettier/recommended',
-  ],
-  overrides: [],
-  parser: '@typescript-eslint/parser',
-  parserOptions: {
-    ecmaVersion: 'latest',
-    sourceType: 'module',
-  },
-  plugins: ['react', 'unused-imports'],
-  rules: {
-    'react/prop-types': 'off',
-    'unused-imports/no-unused-imports': 'error',
-    'react/react-in-jsx-scope': 'off',
-    '@typescript-eslint/no-explicit-any': 'warn',
-    '@typescript-eslint/no-unused-vars': 'warn',
-    '@typescript-eslint/no-unused-expressions': 'warn',
-    'prettier/prettier': [
-      'error',
-      {
-        endOfLine: 'auto',
-      },
-    ],
-  },
-  settings: {
-    'import/parsers': {
-      '@typescript-eslint/parser': ['.ts', '.tsx'],
-    },
-    react: {
-      version: 'detect',
-    },
-    'import/resolver': {
-      node: {
-        paths: ['src'],
-        extensions: ['.js', '.jsx', '.ts', '.tsx'],
-      },
-    },
-  },
-};

frontend/eslint.config.js

@@ -0,0 +1,78 @@
+import js from '@eslint/js'
+import tsParser from '@typescript-eslint/parser'
+import tsPlugin from '@typescript-eslint/eslint-plugin'
+import react from 'eslint-plugin-react'
+import unusedImports from 'eslint-plugin-unused-imports'
+import prettier from 'eslint-plugin-prettier'
+import globals from 'globals'
+
+export default [
+  {
+    ignores: [
+      'node_modules/',
+      'dist/',
+      'prettier.config.cjs',
+      '.eslintrc.cjs',
+      'env.d.ts',
+      'public/',
+      'assets/',
+      'vite-env.d.ts',
+      '.prettierignore',
+      'package-lock.json',
+      'package.json',
+      'postcss.config.cjs',
+      'tailwind.config.cjs',
+      'tsconfig.json',
+      'tsconfig.node.json',
+      'vite.config.ts',
+    ],
+  },
+  {
+    files: ['**/*.{js,jsx,ts,tsx}'],
+    languageOptions: {
+      ecmaVersion: 'latest',
+      sourceType: 'module',
+      parser: tsParser,
+      parserOptions: {
+        ecmaFeatures: {
+          jsx: true,
+        },
+      },
+      globals: {
+        ...globals.browser,
+        ...globals.es2021,
+        ...globals.node,
+      },
+    },
+    plugins: {
+      '@typescript-eslint': tsPlugin,
+      react,
+      'unused-imports': unusedImports,
+      prettier,
+    },
+    rules: {
+      ...js.configs.recommended.rules,
+      ...tsPlugin.configs.recommended.rules,
+      ...react.configs.recommended.rules,
+      ...prettier.configs.recommended.rules,
+      'react/prop-types': 'off',
+      'unused-imports/no-unused-imports': 'error',
+      'react/react-in-jsx-scope': 'off',
+      'no-undef': 'off',
+      '@typescript-eslint/no-explicit-any': 'warn',
+      '@typescript-eslint/no-unused-vars': 'warn',
+      '@typescript-eslint/no-unused-expressions': 'warn',
+      'prettier/prettier': [
+        'error',
+        {
+          endOfLine: 'auto',
+        },
+      ],
+    },
+    settings: {
+      react: {
+        version: 'detect',
+      },
+    },
+  },
+]