hive-forge: fix stale-branches comment/docs — hyperhive rebase+ff merges, not squash

hive-forge/src/verbs/lint.rs

@@ -286,9 +286,11 @@ fn run_stale_branches(client: &Client, args: StaleBranchesArgs) -> Result<()> {
     // a closed one tells a surviving stale branch its actual fate —
     // merged (branch is a leftover copy, safe to delete) vs. closed
     // unmerged / never had a PR (the branch is the only copy). Because
-    // hyperhive squash-merges, a merged branch's tip is never an
-    // ancestor of main, so ancestry can't tell these apart; this is the
-    // only signal that can.
+    // hyperhive merges via rebase + fast-forward, the branch's commits
+    // are replayed onto main's current tip as new commits before main
+    // moves — so the original branch tip's SHA is never an ancestor of
+    // main even once merged, and ancestry can't tell these apart; this
+    // is the only signal that can.
     // Whether the walk below hit `MAX_PAGES` without ever seeing a
     // short page — i.e. there are more PRs than the cap fetched, so
     // `latest_pr_by_head` is missing an unknown number of the oldest