fix(maps): 画布因果连线零绘制(节点双键注册) + 战略回顾 total_hold 未初始化 500

- StrategyLayer.vue: setNodeRef 双键注册(渲染键 layer-index 与数据键 layer:目标名)，$el 归一化为 DOM，卸载时清理数据键
- maps.py: total_hold 初始化 0 + summary.hold 透出（修复 review?level=strategic 500 UnboundLocalError）
- tests: 新增 test_maps_review_hold_20261022.py（待核/普通/空/NULL/无level 五例，负对照已验证会失败）

任务: project-20261022-cma-map-canvas-connections-not-drawn-fullstack
阶段A候选件；未 push、未部署（等阶段B放行）

backend/app/api/maps.py

@@ -1305,6 +1305,7 @@ def get_map_review(map_id: int, level: Optional[str] = None, db: Session = Depen
     total_ok = 0
     total_warn = 0
     total_err = 0
+    total_hold = 0  # C1 数据待核计数（此前漏初始化 → 命中 hold_reason 即 UnboundLocalError → review 500）
     total_obj_count = 0
     focus_items = []
 
@@ -1444,6 +1445,7 @@ def get_map_review(map_id: int, level: Optional[str] = None, db: Session = Depen
             "green": total_ok,
             "yellow": total_warn,
             "red": total_err,
+            "hold": total_hold,
             "health_score": round(total_ok / total_obj_count * 100, 1) if total_obj_count > 0 else 0,
         },
         "focus_items": focus_items,