F-catalog-B: registry_mirrors reads distribution's mirrors, asks one again and drops one by hand

The state mirrors had no read tool and no ask-again (seams review note 1): a copy a follower holds and
does not end could only wait for a restart. registry_mirrors lists each kept copy and its claim, asks one
again with its claim let go, and drops one, saying refused under the ask's id so its waiter ends.

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

modules/distribution/module.json

@@ -48,6 +48,7 @@
     "registry_health",
     "registry_holds",
     "registry_incoming",
+    "registry_mirrors",
     "registry_old_name"
   ],
   "invokes": [