feat: rename skills/skiff to pouch and move ACK state under .pouch

Use ~/.pouch, the pouch CLI, and .pouch.yaml as the SSOT container.
Keep the inner skills/ packages, and store ACK project state in
.pouch/ack instead of docs/ack.

skills/ack/scripts/validate_tasks.py

@@ -763,17 +763,17 @@ def validate_builtin(data: dict) -> list[str]:
                     )
         if (
             "knowledgeFile" in project
-            and project.get("knowledgeFile") != "docs/ack/knowledge.yaml"
+            and project.get("knowledgeFile") != ".pouch/ack/knowledge.yaml"
         ):
             errors.append(
-                "project.knowledgeFile 必须固定为 docs/ack/knowledge.yaml"
+                "project.knowledgeFile 必须固定为 .pouch/ack/knowledge.yaml"
             )
         if (
             "deliveryFile" in project
-            and project.get("deliveryFile") != "docs/ack/delivery.yaml"
+            and project.get("deliveryFile") != ".pouch/ack/delivery.yaml"
         ):
             errors.append(
-                "project.deliveryFile 必须固定为 docs/ack/delivery.yaml"
+                "project.deliveryFile 必须固定为 .pouch/ack/delivery.yaml"
             )
         if "deliveryFile" in project and not isinstance(data.get("deliveryRuns"), list):
             errors.append("引用 deliveryFile 的任务板必须包含 deliveryRuns 列表")