Replace @tiptap/markdown's beta contentType: "markdown" parser with a
dedicated marked-based HTML pipeline for loading markdown content.
The @tiptap/markdown parser silently drops content in complex documents
(tables, nested lists, mentions). Instead, we now:
1. Pre-convert mention links to <span data-type="mention"> HTML
2. Render markdown to HTML via a dedicated Marked instance with a custom
renderer that wraps table cell content in <p> tags (required by
Tiptap's TableCell block+ content spec)
3. Load as HTML — Tiptap's ProseMirror HTML parser handles everything
4. Keep @tiptap/markdown extension only for getMarkdown() serialization
Also adds Table extension support and aligns CSS with the old Markdown
component's minimal mode styling.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
