nisse-review: one unlistable repository holds up no other

Found at bring-up: an empty private repository's /pulls answered 404, and
intake stopped there, so the whole round failed and nothing was reviewed.
A repository whose PRs can't be listed is now logged (intake.repo_failed)
and skipped for the round; its items stay as they are.

Also, from nisse-review's review of this PR: a two-page test pins the
search listing the patterns rest on.

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

nisse-review/src/nisse_review/scheduler.py

@@ -106,8 +106,16 @@ class Scheduler:
             repos = reviewed(self._gitea, self._patterns, self._oplog)
         open_items = {i.id: i for i in self._store.work_items("open")}
         for repo in repos:
+            try:
+                prs = self._gitea.open_pull_requests(repo)
+            except GiteaError as exc:
+                # One repository Gitea won't list (an empty one, one without
+                # pull requests) holds up none of the others; its items stay
+                # as they are.
+                self._oplog.emit("intake.repo_failed", cause=str(exc)[:300], repo=repo)
+                continue
             seen: set[str] = set()
-            for pr in self._gitea.open_pull_requests(repo):
+            for pr in prs:
                 key = item_id(repo, pr.number)
                 seen.add(key)
                 self._see(open_items.get(key), repo, pr)