feat: convert to Next.js with TypeScript and Tailwind CSS

Replace vanilla HTML/JS/CSS with Next.js App Router, TypeScript,
and Tailwind CSS. Responsive design with dark mode support.
All original game logic preserved: grid generation, click-to-cross,
localStorage persistence.

web/package.json

@@ -0,0 +1,26 @@
+{
+  "name": "nextjs-temp",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "dev": "next dev",
+    "build": "next build",
+    "start": "next start",
+    "lint": "eslint"
+  },
+  "dependencies": {
+    "next": "16.2.2",
+    "react": "19.2.4",
+    "react-dom": "19.2.4"
+  },
+  "devDependencies": {
+    "@tailwindcss/postcss": "^4",
+    "@types/node": "^20",
+    "@types/react": "^19",
+    "@types/react-dom": "^19",
+    "eslint": "^9",
+    "eslint-config-next": "16.2.2",
+    "tailwindcss": "^4",
+    "typescript": "^5"
+  }
+}