Trigger an app's reconcile sweep

Hands the app every live artifact of its own kinds in this account, as {id, metadata}, so it can release backing resources for anything it is still holding that the registry no longer has a row for.

The set is the contract, so it is never truncated. A partial set reads to the app as "everything else is an orphan", which for a sweeping handler means deleting live data. If the account holds more artifacts of these kinds than one sweep can carry, this refuses rather than sending a prefix — which is why the size check is part of the 202, not of the sweep.

202, and the sweep runs after the response. A reconcile walks an app's whole backing store for the account, so holding the request open for it would tie an operator's timeout to an object-store scan. What is decided before the 202 is everything a caller can act on: that the app is installed, and that its live set fits. The registry logs a reported outcome after acceptance; legacy handlers remain unreported.

live_count is what distinguishes a sweep of four hundred artifacts from a sweep of an app the account owns nothing of — which is usually a mistake in which app was named.

Requires the same install permission the other lifecycle verbs do. A sweep tells an app what the registry no longer holds, which a sweeping handler acts on by deleting its own backing data — so this is a write verb, and it used to be gated as a read.