Merge duplicate reports into this one

Fold one or more duplicate reports into this report, which survives. The sources' signals, work-log artefacts, pull requests, task runs and checks move onto the survivor, the survivor's signal counters take on theirs, and each source is archived with a 'duplicate of' link back to the survivor. A source's open pull request stays open, because the survivor holds it after the move. Pick the survivor deliberately: prefer the older report, and prefer the one with an open implementation PR or an active claim. Any active claim on a source is released, so re-claim the survivor if you were working on one. Titles and summaries are not combined, so edit it afterwards if it needs a rewrite. A merged report keeps its URL but cannot be restored, because its signals now belong to the survivor.