use only one markdown processing pipeline

Removes marked in favor of remark which is already used by astro.

package.json

@@ -18,14 +18,15 @@
     "@types/node": "^20.14.11",
     "astro": "^4.15.9",
     "astro-breadcrumbs": "^2.3.1",
-    "marked": "^14.1.0",
-    "marked-alert": "^2.0.2",
     "node": "npm:22.7.0",
+    "rehype-stringify": "^10.0.1",
     "remark-github-blockquote-alert": "^1.2.1",
     "remark-parse": "^11.0.0",
+    "remark-rehype": "^11.1.1",
     "solid-devtools": "^0.30.1",
     "solid-js": "^1.8.18",
-    "typescript": "^5.5.3"
+    "typescript": "^5.5.3",
+    "unified": "^11.0.5"
   },
   "devDependencies": {
     "@astrojs/ts-plugin": "^1.10.2",