feat(MarkdownEditor): integrate Mermaid support for diagram rendering in Markdown

- Added MermaidRenderer component to handle Mermaid diagrams within Markdown content.
- Enhanced preformatted code block handling to detect and render Mermaid syntax.
- Updated package.json and package-lock.json to include Mermaid dependency for diagram support.

package.json

@@ -37,6 +37,7 @@
     "emoji-mart": "^5.6.0",
     "emoji-regex": "^10.5.0",
     "lucide-react": "^0.544.0",
+    "mermaid": "^11.12.0",
     "next": "15.5.3",
     "next-auth": "^4.24.11",
     "prisma": "^6.16.1",