nisse-review: a new head's review waits for its CI

A review judges the CI result (R1), so a new head's review now waits while
its checks are pending, and starts once they finish, passed or failed. It
also keeps reviews off a GPU that CI is using: #154's first review ran
beside CI's end-to-end job and took about 30 minutes.

- Pending: waits up to tuning.review.ci_wait_s (1 h), then reviews anyway.
- No checks: waits tuning.review.ci_grace_s (2 min) for them to appear,
  then reviews.
- A PR waiting on CI holds up no other: the oldest settled one goes first.
- The head's first sighting is kept on the item (seen_at).

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

nisse-review/tests/review_fakes.py

@@ -73,6 +73,7 @@ class FakeGitea:
     # Readable but not given (public, no grant): missing from /user/repos.
     public: set[str] = field(default_factory=set)
     unlisted: set[str] = field(default_factory=set)  # its PRs can't be listed
+    ci: dict[str, str] = field(default_factory=dict)  # head -> checks; success
 
     def _up(self) -> None:
         if self.down:
@@ -124,7 +125,7 @@ class FakeGitea:
         return []
 
     def checks(self, repo: str, sha: str) -> str:
-        return "success"
+        return self.ci.get(sha, "success")
 
     def archive(self, repo: str, ref: str) -> bytes:
         return archive(self.files)