Artifact listing is paged and includes artifacts shared with you

What

Artifacts are pages and documents created in your account. Listing them has changed:

• The list now comes from /api/frame/artifacts with kind=page,document and sort=last_viewed, fetching your own ("mine") and shared lists at the same time.
• It accepts a pageToken, made of the mine and shared tokens joined by ~, and returns a nextPageToken for the next page.
• The shared list is also read from /api/frame/frames?rel=shared, and results are de-duplicated by slug.
• If the paged endpoint is not available, it falls back to the old /api/frame/frames path, which rejects any pageToken with page_unserved.
• Two feature names, artifact_list_shared_lane and artifact_list_paged, were added to the list of artifact features.
• displayName was added to a list of plugin and MCP fields.

Before, the listing was a single /api/frame/frames?limit= call with no paging.

Why

If you have many artifacts you can now page through all of them, and artifacts others shared with you show up in the list.