Start a pass merging the entities extraction wrote more than once

Queues one deduplication pass over the entity types the collection's subscribed packages declare an identity for and the classes the collection defines itself. Extraction reads each document alone and cannot know what an earlier document already named, so any type standing for a thing that exists once arrives spelled several ways; this resolves them. Merges that would lose attributes or collapse a relation into a self-loop are refused and reported rather than forced. Returns immediately with a job status to poll. Each block's merges commit as they land, so a cancelled or failed pass keeps the merges it made and a second pass continues from there.