Enqueues a background job that re-fetches the bank accounts exposed by this
credential and refreshes their capability data. Use it to repopulate stale
account/permission information without deleting and recreating the key.

The job runs asynchronously — this endpoint only acknowledges the enqueue and
responds 202 Accepted. Requests are debounced: if a sync was already enqueued
for this key within the last 30 seconds, the request is a no-op and the
response carries enqueued: false (still 202). This protects the upstream
bank from rapid retries.