feat(editor): add mermaid code preview (#13456)

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src="https://github.com/user-attachments/assets/eff3e6d5-3129-42ac-aceb-994c18f675ab"
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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Mermaid diagram previews for code blocks with interactive zoom, pan,
and reset controls.
* Improved rendering feedback with loading, error states, retry
behavior, and fallback messaging.

* **Chores**
  * Added Mermaid as a frontend dependency to enable diagram rendering.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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Co-authored-by: L-Sun <zover.v@gmail.com>

packages/frontend/core/package.json

@@ -74,6 +74,7 @@
     "lit": "^3.2.1",
     "lodash-es": "^4.17.21",
     "lottie-react": "^2.4.0",
+    "mermaid": "^10.9.1",
     "mp4-muxer": "^5.2.1",
     "nanoid": "^5.0.9",
     "next-themes": "^0.4.4",