chore: upgrade all deps and fix security vulnerabilities (#350)

Bump VitePress to 2.0.0-alpha.19, TypeScript to 7, and Vite/esbuild overrides
to latest. Pin postcss and nanoid to patched versions to resolve high-severity
audit findings; drop the temporary @vueuse 14.2.1 overrides now that upstream
ships 14.4.0.

package.json

@@ -2,6 +2,9 @@
   "name": "advanced-java",
   "private": true,
   "packageManager": "pnpm@10.33.0",
+  "engines": {
+    "node": "^20.19.0 || >=22.12.0"
+  },
   "scripts": {
     "docs:dev": "vitepress dev docs",
     "docs:build": "vitepress build docs",
@@ -12,15 +15,15 @@
     "vitepress-plugin-comment-with-giscus": "^1.1.15"
   },
   "devDependencies": {
-    "typescript": "^6.0.3",
-    "vitepress": "2.0.0-alpha.17"
+    "typescript": "^7.0.2",
+    "vitepress": "2.0.0-alpha.19"
   },
   "pnpm": {
     "overrides": {
-      "vite": "7.3.5",
-      "esbuild": "0.28.1",
-      "@vueuse/core": "14.2.1",
-      "@vueuse/integrations": "14.2.1"
+      "vite": "8.2.2",
+      "esbuild": "0.28.2",
+      "postcss": "8.5.26",
+      "nanoid": "3.3.18"
     },
     "onlyBuiltDependencies": [
       "esbuild"