Migrate from tiptap-markdown to official @tiptap/markdown

[jbourdin]

Context

The CMS rich text editor uses the community tiptap-markdown package (v0.9.0) for bidirectional markdown support. This package has a confirmed, unfixed bug where markdown pipe tables are not parsed into editable ProseMirror table nodes — they render visually but cells are not interactive (GitHub issues #81, #95). The package is effectively abandoned (no maintainer activity on open issues).

Tiptap v3 ships an official @tiptap/markdown package (v3.22.3) with native table support and a different extension API (parseMarkdown/renderMarkdown on each extension instead of addStorage().markdown.serialize/parse).

Scope

Migrate from tiptap-markdown to @tiptap/markdown. This requires:

1. Install @tiptap/markdown and remove tiptap-markdown
2. Rewrite 5 custom extensions to the new parseMarkdown/renderMarkdown API:
   • ArchetypeReference — [[archetype:slug]] syntax
   • CardReference — [[card:SET-NUM]] syntax
   • DeckReference — [[deck:SHORT_TAG]] syntax
   • HeadingWithId — Pandoc-style {#id} anchors
   • ResizableImage — Pandoc-style {.class style="..."} attributes
3. Update MarkdownEditor.tsx — replace the Markdown import and config
4. Verify table round-trip — pipe tables must parse into editable ProseMirror table nodes and serialize back correctly
5. Verify all custom tags — [[card:...]], [[archetype:...]], [[deck:...]] must round-trip correctly
6. Update tests in assets/test/

References

• Official docs: https://tiptap.dev/docs/editor/markdown
• Custom extension integration: parseMarkdown(token, helpers) / renderMarkdown(node, helpers)
• Current custom extensions: assets/extensions/
• Current editor: assets/components/MarkdownEditor.tsx

Acceptance criteria

• Markdown pipe tables are parsed into editable ProseMirror table nodes in the RTE
• All custom reference tags ([[card:...]], [[archetype:...]], [[deck:...]]) round-trip correctly
• Pandoc-style heading anchors and image attributes round-trip correctly
• All existing frontend tests pass
• No regression in markdown content for existing CMS pages