Scaffold the admin PWA React shell (task 0df715b5)

Add a self-contained Vite + React + TypeScript app under admin/ that
matches the frontend/ toolchain style (vite 7, typescript 5.9, strict
TS). The app shell renders the NestQuest Admin title and the four
placeholder tabs (Today, Tasks, Schedule, History) with mobile-first
CubeCraft styling for the 390x844 reference.

- package.json scripts: dev, build, preview, test
- Vitest + jsdom + @testing-library/react smoke test proving the shell
  renders all four tab labels and switches the active tab
- commit admin/package-lock.json; ignore admin/node_modules and
  admin/dist

admin/package.json

@@ -0,0 +1,27 @@
+{
+  "name": "nestquest-admin",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vite build",
+    "preview": "vite preview",
+    "test": "vitest run"
+  },
+  "dependencies": {
+    "react": "^19.2.0",
+    "react-dom": "^19.2.0"
+  },
+  "devDependencies": {
+    "@testing-library/dom": "^10.4.1",
+    "@testing-library/react": "^16.3.0",
+    "@types/react": "^19.2.0",
+    "@types/react-dom": "^19.2.0",
+    "@vitejs/plugin-react": "^5.0.0",
+    "jsdom": "^30.1.1",
+    "typescript": "^5.9.2",
+    "vite": "^7.1.5",
+    "vitest": "^3.2.4"
+  }
+}