feat(pipeline): Pipeline 图持久化 — GraphStore 实现

新增 GraphStore trait 和 MemoryGraphStore 实现:
- save/load/delete/list_ids 异步接口
- 可选文件持久化到 JSON 目录
- 启动时从磁盘加载已保存的图

SkillOrchestrationDriver 集成:
- 新增 with_graph_store() 构造函数
- graph_id 路径从硬编码错误改为从 GraphStore 查找
- 无 store 时返回明确的错误信息

修复了 "Graph loading by ID not yet implemented" 的 TODO

crates/zclaw-pipeline/src/actions/orchestration.rs

@@ -13,12 +13,22 @@ use super::OrchestrationActionDriver;
 pub struct SkillOrchestrationDriver {
     /// Skill registry for executing skills
     skill_registry: Arc<zclaw_skills::SkillRegistry>,
+    /// Graph store for persisting/loading graphs by ID
+    graph_store: Option<Arc<dyn zclaw_skills::orchestration::GraphStore>>,
 }
 
 impl SkillOrchestrationDriver {
     /// Create a new orchestration driver
     pub fn new(skill_registry: Arc<zclaw_skills::SkillRegistry>) -> Self {
-        Self { skill_registry }
+        Self { skill_registry, graph_store: None }
+    }
+
+    /// Create with graph persistence
+    pub fn with_graph_store(
+        skill_registry: Arc<zclaw_skills::SkillRegistry>,
+        graph_store: Arc<dyn zclaw_skills::orchestration::GraphStore>,
+    ) -> Self {
+        Self { skill_registry, graph_store: Some(graph_store) }
     }
 }
 
@@ -38,8 +48,11 @@ impl OrchestrationActionDriver for SkillOrchestrationDriver {
             serde_json::from_value::<SkillGraph>(graph_value.clone())
                 .map_err(|e| format!("Failed to parse graph: {}", e))?
         } else if let Some(id) = graph_id {
-            // Load graph from registry (TODO: implement graph storage)
-            return Err(format!("Graph loading by ID not yet implemented: {}", id));
+            // Load graph from store
+            self.graph_store.as_ref()
+                .ok_or_else(|| "Graph store not configured. Cannot resolve graph_id.".to_string())?
+                .load(id).await
+                .ok_or_else(|| format!("Graph not found: {}", id))?
         } else {
             return Err("Either graph_id or graph must be provided".to_string());
         };