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/select_tasks.py

@@ -197,7 +197,7 @@ def _parser() -> argparse.ArgumentParser:
     parser.add_argument(
         "tasks",
         nargs="?",
-        default="docs/ack/tasks.yaml",
+        default=".pouch/ack/tasks.yaml",
         help="任务板路径",
     )
     parser.add_argument("--task-id", action="append", default=[])