feat: add tldraw drawing canvas support for .tldr files

[Adityakk9031]

Resolves #696

Description

This PR introduces native support for drawing canvases within the OpenKnowledge editor using the tldraw library. Users can now create, open, and edit infinite canvas drawing boards by opening files with .tldr, .tldraw, or .okdraw extensions.

What Changed

• Core Extension Support: Added .tldr file extensions to LINKABLE_ASSET_EXTENSIONS and implemented the isTldrawDocFile helper.
• Tldraw Editor Component: Implemented TldrawDocEditor.tsx in packages/app. It renders the <Tldraw> canvas and serializes/deserializes canvas snapshots directly to the underlying Y.Text('source') doc string.
• Activity Pool Integration: Configured EditorActivityPool.tsx to mount the TldrawDocEditor component when a .tldr document is active.
• Dependencies: Added tldraw dependency to packages/app.

Testing

• Created a file named canvas.tldr and verified that the tldraw editor loaded correctly.
• Added shapes and lines to the canvas, refreshed, and verified that all progress persisted.
• Verified that the codebase successfully compiles and passes Typechecking.

[Adityakk9031]

@tim-inkeep have a look