Suppress Mermaid render error artifacts

[codenem]

Summary

• Add a shared Mermaid renderer that enables suppressErrorRendering and cleans up Mermaid's fallback error node.
• Route failed Mermaid renders through the product toast flow with a safe inline fallback instead of raw Mermaid error text.
• Apply the same Mermaid error suppression to generated document HTML.

Validation

• npm --workspace @probo/ui run lint
• npm --workspace @probo/ui run check (fails on existing src/Foundation.stories.tsx(193,16) missing socialName, unrelated to this change)
• make go-fmt

Notes

• npm install was required in this cloud environment because dependencies were not installed; the local Node 22/npm 10 toolchain emitted an engine warning for the repo's Node 24/npm 11 requirement.

Linear Issue: ENG-438

  

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Summary by cubic

Prevents raw mermaid error text from appearing in the editor, Markdown preview, and generated docs. Adds a shared renderer in @probo/ui that suppresses mermaid error nodes, shows a toast on failure, and falls back to safe inline content (ENG-438).

Package: ui +104 -28

• Added shared renderMermaidDiagram helper that initializes mermaid with suppressErrorRendering and removes its fallback error node; exported mermaidRenderErrorToast.
• Updated MermaidDiagram and rich editor MermaidNodeView to use the helper; on failure, show a toast and render a safe inline fallback instead of raw error text.

Service +1 -1

• Updated docgen template to initialize mermaid with suppressErrorRendering so exported HTML never shows Mermaid’s error output.

^{Written for commit cc8c47f. Summary will update on new commits.}