feat(static): improve nextjs static example

- upgrade all dependencies
- upgrade to Tailwind CSS v4
- remove ugly default background
- remove unnecessary default content
- clean up files and remove those that are no longer needed

nextjs/spa/package.json

@@ -1,6 +1,6 @@
 {
-  "name": "nextjs",
-  "version": "0.1.0",
+  "name": "nextjs-spa",
+  "version": "0.0.0",
   "private": true,
   "scripts": {
     "dev": "next dev",
@@ -9,19 +9,19 @@
     "lint": "next lint"
   },
   "dependencies": {
-    "react": "^18",
-    "react-dom": "^18",
-    "next": "14.1.4"
+    "@tailwindcss/postcss": "^4.1.10",
+    "next": "^15.3.4",
+    "postcss": "^8.5.6",
+    "react": "^19.1.0",
+    "react-dom": "^19.1.0",
+    "tailwindcss": "^4.1.10"
   },
   "devDependencies": {
-    "typescript": "^5",
-    "@types/node": "^20",
-    "@types/react": "^18",
-    "@types/react-dom": "^18",
-    "autoprefixer": "^10.0.1",
-    "postcss": "^8",
-    "tailwindcss": "^3.3.0",
-    "eslint": "^8",
-    "eslint-config-next": "14.1.4"
+    "@types/node": "^24.0.3",
+    "@types/react": "^19.1.8",
+    "@types/react-dom": "^19.1.6",
+    "eslint": "^9.29.0",
+    "eslint-config-next": "^15.3.4",
+    "typescript": "^5.8.3"
   }
 }