Add TypeScript to app-frontend (#2364)

* Add TypeScript to app-frontend

Co-authored-by: Evan Song <52982404+ferothefox@users.noreply.github.com>

* Switch app-frontend to ESLint 9 & Nuxt config

* Fix ESLint issues after config change in app-frontend

---------

Co-authored-by: Evan Song <52982404+ferothefox@users.noreply.github.com>

apps/app-frontend/eslint.config.mjs

@@ -0,0 +1,22 @@
+import { createConfigForNuxt } from '@nuxt/eslint-config/flat'
+import { fixupPluginRules } from '@eslint/compat'
+import turboPlugin from 'eslint-plugin-turbo'
+
+export default createConfigForNuxt().append([
+  {
+    name: 'turbo',
+    plugins: {
+      turbo: fixupPluginRules(turboPlugin),
+    },
+    rules: {
+      'turbo/no-undeclared-env-vars': 'error',
+    },
+  },
+  {
+    name: 'modrinth',
+    rules: {
+      'vue/html-self-closing': 'off',
+      'vue/multi-word-component-names': 'off',
+    },
+  },
+])