feat(task3): migrate toolchain to oxfmt + oxlint

- Install oxfmt with .oxfmtrc.json (maps Prettier config)
- Install oxlint with oxlint.config.ts (TypeScript + React rules)
- Replace admin ESLint with oxlint
- Remove Prettier integration from server ESLint (keep ESLint for type checking)
- Delete server .prettierrc and admin eslint.config.js

apps/server/eslint.config.mjs

@@ -1,6 +1,5 @@
 // @ts-check
 import eslint from '@eslint/js';
-import eslintPluginPrettierRecommended from 'eslint-plugin-prettier/recommended';
 import globals from 'globals';
 import tseslint from 'typescript-eslint';
 
@@ -10,7 +9,6 @@ export default tseslint.config(
   },
   eslint.configs.recommended,
   ...tseslint.configs.recommendedTypeChecked,
-  eslintPluginPrettierRecommended,
   {
     languageOptions: {
       globals: {
@@ -29,7 +27,6 @@ export default tseslint.config(
       '@typescript-eslint/no-explicit-any': 'off',
       '@typescript-eslint/no-floating-promises': 'warn',
       '@typescript-eslint/no-unsafe-argument': 'warn',
-      "prettier/prettier": ["error", { endOfLine: "auto" }],
     },
   },
 );