feat: enable mermaid charts (#134)

Enables projects to add [Mermaid](https://mermaid.js.org/) charts and
diagrams to their docs.

Author: ilbertt

deno.json

@@ -16,8 +16,10 @@
     "@radix-ui/react-navigation-menu": "npm:@radix-ui/react-navigation-menu@^1.2.14",
     "@types/react": "npm:@types/react@^19.1.12",
     "astro-integration-kit": "npm:astro-integration-kit@^0.19.0",
+    "astro-mermaid": "npm:astro-mermaid@^1.1.0",
     "fs": "node:fs",
     "json-schema-to-typescript": "npm:json-schema-to-typescript@^15.0.4",
+    "mermaid": "npm:mermaid@^11.12.0",
     "pagefind": "npm:pagefind@^1.4.0",
     "react": "npm:react@^19.1.1",
     "react-dom": "npm:react-dom@^19.1.1",