nisse-review marks a reply that settles its thread; the PR's author resolves it

The reviewer is read-only (R3), so Gitea refuses it resolving a thread.
Now each reply says whether it settles its thread, and a settled reply
carries <!-- nisse-review: settled -->. nisse-dev, as the author, resolves
every comment on that thread's line when it watches the PR, and doesn't
take the settled reply as a point to answer. scripts/resolve_settled.py
does the same for PRs made by hand.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J5Utyfzw7gF7UhjRDEtjTk

docs/Development-Plan.md

@@ -688,6 +688,13 @@ of earlier points, replies on threads, the round cap and its reset, `stop` and
   to the model to make again (on #166 it didn't, and looped to the turn cap).
   Each reply carries its point's key, so a run re-done after a crash answers
   nothing twice.
+- **Settled threads:** each `reply` says whether it settles its thread (a
+  concession, or an answer or deferral accepted; never while waiting on a
+  change). A settled reply carries `<!-- nisse-review: settled -->`. Being
+  read-only (R3), the reviewer can't resolve the thread, so the PR's author
+  does: nisse-dev resolves every comment on that thread's line when it next
+  watches the PR and takes the settled reply as no point to answer;
+  `scripts/resolve_settled.py` does the same for PRs made by hand.
 - **Sign-off:** `sign_off` posts a short review when there is nothing to raise;
   while it stays happy, a later review offers `still_happy`, which posts nothing
   (operator: no repeated LGTMs).