Spandrel Label Index

  GET /xrpc/com.atproto.label.queryLabels
        ?uriPatterns=<did or at:// uri>   repeatable; at://<did>/...* matches one account's records
        &sources=<labeler did>            optional, repeatable
        &limit=<1-250>                    optional, default 50
        &cursor=<from the previous page>  optional

  GET /health     service info
  GET /labelers   labeler info