Regenerate the admin API document for the fetch phase

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/admin-api.openapi.json

@@ -6485,6 +6485,10 @@
           "percent": {
             "type": "integer",
             "description": "Percent is absent rather than zero when the total is unknown: an invented percentage that stops moving is worse than a byte count that keeps rising."
+          },
+          "phase": {
+            "type": "string",
+            "description": "Phase is empty while the bytes arrive, \"checking\" while a set's files are checked against the mirror's checksums."
           }
         }
       },