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.

pouch/__main__.py

@@ -0,0 +1,4 @@
+from pouch.cli import main
+
+if __name__ == "__main__":
+    main()