chore: migrate to @vigdorov/* shared configs (eslint, prettier, typescript, vite)

Replace project-local ESLint, Prettier, TypeScript, and Vite configs
with shared packages from dev-configs monorepo.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/eslint.config.js

@@ -1,41 +1,3 @@
-import js from '@eslint/js'
-import globals from 'globals'
-import reactHooks from 'eslint-plugin-react-hooks'
-import reactRefresh from 'eslint-plugin-react-refresh'
-import tseslint from 'typescript-eslint'
-import { defineConfig, globalIgnores } from 'eslint/config'
+import {react} from '@vigdorov/eslint-config';
 
-export default defineConfig([
-  globalIgnores(['dist', 'coverage', '*.config.ts', '*.config.js']),
-  {
-    files: ['**/*.{ts,tsx}'],
-    extends: [
-      js.configs.recommended,
-      ...tseslint.configs.strictTypeChecked,
-      reactHooks.configs.flat.recommended,
-      reactRefresh.configs.vite,
-    ],
-    languageOptions: {
-      ecmaVersion: 2020,
-      globals: globals.browser,
-      parserOptions: {
-        projectService: true,
-        tsconfigRootDir: import.meta.dirname,
-      },
-    },
-    rules: {
-      '@typescript-eslint/no-unnecessary-condition': 'error',
-      '@typescript-eslint/prefer-nullish-coalescing': 'error',
-      '@typescript-eslint/no-confusing-void-expression': 'off',
-      '@typescript-eslint/no-misused-promises': [
-        'error',
-        {
-          checksVoidReturn: {
-            attributes: false,
-          },
-        },
-      ],
-      'react-hooks/set-state-in-effect': 'off',
-    },
-  },
-])
+export default react();