Include API-created repositories in scheduled maintenance #108

The authenticated creation API can create a repository under the default access policy without a named configuration entry. Ordinary pushes checkpoint its WAL and maintenance endpoints work, but the host scheduler currently enumerates only named policies, so these repositories are omitted from periodic collection.

Make scheduled maintenance discover API-created repositories without operator edits, using existing object storage and authenticated WAL state. Keep discovery a hint, preserve the WAL head as the only durable authority, and avoid a repository registry or permanently running worker. Cover inactive repositories, interrupted creation and bounded enumeration with local MinIO tests.

Follow-on to #106 and #107. Existing named-repository scheduling is unchanged.