build(astro): migrate site to Astro 6

www/package.json

@@ -3,12 +3,13 @@
   "private": true,
   "type": "module",
   "engines": {
-    "node": ">=20.19.0"
+    "node": ">=22.12.0"
   },
   "scripts": {
     "dev": "astro dev",
-    "build": "astro build",
-    "build:sandbox": "NODE_OPTIONS=--require=./tools/localhost-dns.cjs astro build",
+    "check": "astro check",
+    "build": "astro check && astro build",
+    "build:sandbox": "NODE_OPTIONS=--require=./tools/localhost-dns.cjs astro check && NODE_OPTIONS=--require=./tools/localhost-dns.cjs astro build",
     "preview": "astro preview",
     "extract:blog-footers": "node tools/extract-blog-footers.mjs",
     "crawl:live": "node tools/crawl-live-site.mjs",
@@ -19,13 +20,16 @@
     "generate:redirects": "node tools/generate-redirects.mjs"
   },
   "dependencies": {
-    "@astrojs/mdx": "^4.3.14",
-    "astro": "^5.10.0",
+    "@astrojs/mdx": "^5.0.6",
+    "astro": "^6.4.8",
     "cheerio": "^1.1.0",
     "fast-glob": "^3.3.3",
     "gray-matter": "^4.0.3",
     "swiper": "^12.2.0",
-    "turndown": "^7.2.0",
-    "zod": "^3.25.0"
+    "turndown": "^7.2.0"
+  },
+  "devDependencies": {
+    "@astrojs/check": "^0.9.10",
+    "typescript": "^6.0.3"
   }
 }