Make the user cache work for job entities in the queue.

[scrosby]

Changes proposed in this PR

• Fix create-task-ent to have a :db/id

Why are we making these changes?

task-ent->user uses :db/id as a cache key. However, synthetic tasks entities for pending jobs don't have that and aren't cached. This makes that cache essentially noop for pending jobs; they always miss.

Fix this by borrowing the :db/id of the source job.