chore: update .gitignore, CLAUDE.md, training_log.json, and ml_filter.py

- Added .worktrees/ to .gitignore to prevent tracking of worktree files.
- Marked `optuna-precision-objective-plan` as completed in CLAUDE.md.
- Added new training log entry for a LightGBM model with updated parameters and performance metrics in training_log.json.
- Updated error handling in ml_filter.py to return False on prediction errors instead of True, improving the robustness of the ML filter.

src/ml_filter.py

@@ -149,8 +149,8 @@ class MLFilter:
             )
             return bool(proba >= self._threshold)
         except Exception as e:
-            logger.warning(f"ML 필터 예측 오류 (폴백 허용): {e}")
-            return True
+            logger.warning(f"ML 필터 예측 오류 (진입 차단): {e}")
+            return False
 
     def reload_model(self):
         """외부에서 강제 리로드할 때 사용 (하위 호환)."""