List Canvas Items

Lists the items in the replica's Canvas (files agents drop into ~/.replicas/canvas/). Each item has a kind (markdown, html, image, video, audio, or other) inferred from its extension and a sizeBytes measured at list time. Files larger than 5 MB are still listed; the getReplicaCanvasItem endpoint will return tooLarge: true for them so callers know to fall back to replicas media upload.