Tuning: the CI waits may be zero

The live review test sets ci_grace_s: 0, which the shared tuning parser
refused (every number had to be positive). A field now opts in to zero
with metadata {"zero": True}; ci_wait_s and ci_grace_s do.

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/config.py

@@ -56,9 +56,9 @@ class ReviewTuning:
     diff_chars: int = 60000  # the diff in the review's context; files on demand
     attempts: int = 2  # failed runs on one PR before saying so on it
     # A new head waits for its CI to finish: at most ci_wait_s while checks
-    # are pending, and ci_grace_s for checks to appear at all.
-    ci_wait_s: float = 3600.0
-    ci_grace_s: float = 120.0
+    # are pending, and ci_grace_s for checks to appear at all. 0: don't wait.
+    ci_wait_s: float = field(default=3600.0, metadata={"zero": True})
+    ci_grace_s: float = field(default=120.0, metadata={"zero": True})
 
 
 @dataclass(frozen=True)