enable.post.ts only cleared disabledAt, so toggling a repo off and on
couldn't advance a mapping that never finished enrolling. Now enqueues
tangled.create-repo when there's no mirror yet, with force: false so
it resumes rather than duplicates.
Confined to enable.post.ts, using the existing enqueue/kickWorker
helpers. No schema change, no shared code touched, no user-facing copy.
Tests: full unit suite passes. No tests added, following the same
convention -- enable.post.ts is a route handler, and none are
unit-tested here. The helpers it composes each have their own specs
(queue.spec.ts, kick-worker.spec.ts), but the new "enqueue only when
there's no mirror yet" condition itself is unverified, so that branch
rests on review rather than a test.