ENG-1507: Drag and drop files from wikilinks

[trangdoan982]

https://www.loom.com/share/a321b01e4eee4d40a5fff3554bc88cb5

https://www.loom.com/share/4466009d58cd47a89dade0a908165a7a

Summary

• Adds drag-and-drop support for wikilinks onto tldraw canvases to create discourse node shapes
• Reading view: Makes <a class="internal-link"> elements natively draggable via markdown post-processor
• Live Preview: Uses CM6 mark decorations to add draggable="true" + data-dg-link-path to wikilink spans, with a domEventHandlers({ dragstart }) handler to set obsidian:// drag data
• Supports both wikilinks ([[...]]) and markdown links ([text](path.md))
  🤖 Generated with Claude Code

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[linear-code]

ENG-1507 Ability to drag and drop files from wikilink

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[trangdoan982]

@jsmorabito let me know what you think of this widget approach to allow for wikilink drag. there was techincal difficulty with regular drag action for wikilink as explained in the Loom

[jsmorabito]

This is a fine solution for now, but I think we'll want to revisit it again in the future when we're polishing to make this more seamless and ill take a note down as a reminder for that.

One question: can we detect when a tldraw canvas file is open and only show the drag handle icons when one is? That would make this less intrusive to the user experience

[jsmorabito]

#960 (comment)