chore(frontend): introduce prettier + eslint and prune unused code

- Add Prettier 3 with prettier-plugin-organize-imports (sorts/removes unused imports)
- Add ESLint 10 flat config with typescript-eslint + eslint-plugin-vue + eslint-config-prettier
- Add root scripts: format, format:check, lint, lint:fix
- Reformat 257 files across admin-web, ops-web, desktop-client, packages
- Remove unused locals/exports flagged by --noUnusedLocals/--noUnusedParameters
- Fix duplicate localTabLabel key, surrogate-pair regex u-flag, NBSP literal in regex
- Skip server/ (Go) and apps/browser-extension/ (deprecated per ADR)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

eslint.config.mjs

@@ -0,0 +1,80 @@
+import eslint from '@eslint/js'
+import eslintConfigPrettier from 'eslint-config-prettier'
+import eslintPluginVue from 'eslint-plugin-vue'
+import globals from 'globals'
+import typescriptEslint from 'typescript-eslint'
+
+export default typescriptEslint.config(
+  {
+    ignores: [
+      '**/node_modules/**',
+      '**/dist/**',
+      '**/build/**',
+      '**/out/**',
+      '**/release/**',
+      '**/.output/**',
+      '**/.wxt/**',
+      '**/.vite/**',
+      '**/coverage/**',
+      '**/components.d.ts',
+      '**/auto-imports.d.ts',
+      '**/stats.html',
+      'server/**',
+      'apps/browser-extension/**',
+    ],
+  },
+
+  {
+    extends: [
+      eslint.configs.recommended,
+      ...typescriptEslint.configs.recommended,
+      ...eslintPluginVue.configs['flat/recommended'],
+    ],
+    files: ['**/*.{js,mjs,cjs,ts,tsx,vue}'],
+    languageOptions: {
+      ecmaVersion: 'latest',
+      sourceType: 'module',
+      globals: {
+        ...globals.browser,
+        ...globals.node,
+      },
+      parserOptions: {
+        parser: typescriptEslint.parser,
+        extraFileExtensions: ['.vue'],
+      },
+    },
+    rules: {
+      '@typescript-eslint/no-unused-vars': [
+        'warn',
+        {
+          argsIgnorePattern: '^_',
+          varsIgnorePattern: '^_',
+          caughtErrorsIgnorePattern: '^_',
+        },
+      ],
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/no-empty-object-type': 'off',
+      'vue/multi-word-component-names': 'off',
+      'vue/no-v-html': 'off',
+      'vue/attribute-hyphenation': 'off',
+      'vue/v-on-event-hyphenation': 'off',
+      'vue/require-default-prop': 'off',
+      'no-empty': ['error', { allowEmptyCatch: true }],
+      'no-useless-escape': 'warn',
+      'no-useless-assignment': 'warn',
+      'prefer-const': ['error', { ignoreReadBeforeAssign: true }],
+    },
+  },
+
+  {
+    files: ['**/*.{test,spec}.{ts,tsx,js}'],
+    languageOptions: {
+      globals: {
+        ...globals.node,
+        ...globals.jest,
+      },
+    },
+  },
+
+  eslintConfigPrettier,
+)