Store DAG plan to IPFS and track plan_cid in run_cache

- Add plan_cid column to run_cache schema
- Store DAG JSON to IPFS during execute_dag task
- Return plan_cid in run status and list APIs

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

legacy_tasks.py

@@ -382,6 +382,17 @@ def execute_dag(self, dag_json: str, run_id: str = None) -> dict:
         import asyncio
         import database
 
+        # Store plan (DAG) to IPFS
+        plan_cid = None
+        try:
+            import ipfs_client
+            dag_dict = json.loads(dag_json)
+            plan_cid = ipfs_client.add_json(dag_dict)
+            if plan_cid:
+                logger.info(f"Stored plan to IPFS: {plan_cid}")
+        except Exception as e:
+            logger.warning(f"Failed to store plan to IPFS: {e}")
+
         async def save_to_db():
             if database.pool is None:
                 await database.init_db()
@@ -409,6 +420,7 @@ def execute_dag(self, dag_json: str, run_id: str = None) -> dict:
                     inputs=input_hashes_for_db,
                     ipfs_cid=output_ipfs_cid,
                     actor_id=actor_id,
+                    plan_cid=plan_cid,
                 )
 
                 # Save output as media for the user