fix: handle None judge_score in generate_manifest.py

judge_score key can exist with None value in task results. Changed
`"judge_score" in info` to `info.get("judge_score") is not None` to
prevent TypeError during MANIFEST aggregation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sjarmak

scripts/generate_manifest.py

@@ -665,7 +665,7 @@ def main():
             if info["status"] != "errored":
                 total_reward += info["reward"]
 
-            if "judge_score" in info:
+            if info.get("judge_score") is not None:
                 judge_score_sum += info["judge_score"]
                 judge_count += 1