chore(demo): update Astro to v5.3.0 and other dependencies (#203)

Update demo dependencies to latest version, including Astro and astro-portabletext

Author: theisel

demo/package.json

@@ -13,10 +13,10 @@
   "dependencies": {
     "@astrojs/solid-js": "^5.0.4",
     "@astrojs/svelte": "^7.0.4",
-    "astro": "^5.2.5",
-    "astro-portabletext": "^0.11.0",
+    "astro": "^5.3.0",
+    "astro-portabletext": "^0.11.1",
     "solid-js": "^1.9.4",
-    "svelte": "^5.19.9"
+    "svelte": "^5.20.1"
   },
   "engines": {
     "node": "^18.17.1 || ^20.3.0 || >=22.0.0"