nisse-review: later reviews, replies, rounds, stop and review (M7.5)

Back on a PR it reviewed: a new head gets a later review of the commits
since (each one's diff, through the API) and of its earlier points; what
was said since gets replies, answered where it was said or skipped with a
reason. It signs off once and stays quiet while still happy. Past
tuning.review.max_rounds it sums up for the operator and goes quiet,
until a push or someone other than the PR's author joins in. An
operator's `stop` quiets it; `review` asks for a fresh review.

Reviews carry numbered markers and replies their point's key, so
recovery posts nothing twice.

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

nisse-review.example.yaml

@@ -36,6 +36,6 @@ gitea:
 
 # tuning:                             # docs/Tuning-Guide.md
 #   review: {poll_s: 60, max_turns: 40, diff_chars: 60000, attempts: 2,
-#            ci_wait_s: 3600, ci_grace_s: 120}
+#            ci_wait_s: 3600, ci_grace_s: 120, max_rounds: 4}
 #   expert: {consult_budget: 3}
 #   context: {keep_recent_turns: 6, safety_margin: 0.1}