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/templates/tasks.schema.json

@@ -1,6 +1,6 @@
 {
   "$schema": "http://json-schema.org/draft-07/schema#",
-  "$id": "https://git.yumee.top/laily/skills/skills/ack/templates/tasks.schema.json",
+  "$id": "https://git.yumee.top/laily/pouch/skills/ack/templates/tasks.schema.json",
   "title": "ACK task board",
   "description": "tasks.yaml 的权威结构。跨语言可用；参考校验实现见 scripts/validate_tasks.py。",
   "type": "object",
@@ -45,7 +45,7 @@
         "repoPath": {
           "type": "string",
           "deprecated": true,
-          "description": "Legacy informational field; ACK derives project files from --project-root/docs/ack"
+          "description": "Legacy informational field; ACK derives project files from --project-root/.pouch/ack"
         },
         "baseUrl": {
           "type": "string"
@@ -57,16 +57,16 @@
         },
         "overlayFile": {
           "type": "string",
-          "description": "项目覆盖层文件路径，默认 docs/ack/project.md，可自定义"
+          "description": "项目覆盖层文件路径，默认 .pouch/ack/project.md，可自定义"
         },
         "knowledgeFile": {
           "type": "string",
-          "const": "docs/ack/knowledge.yaml",
+          "const": ".pouch/ack/knowledge.yaml",
           "description": "项目知识护栏库的唯一权威路径"
         },
         "deliveryFile": {
           "type": "string",
-          "const": "docs/ack/delivery.yaml",
+          "const": ".pouch/ack/delivery.yaml",
           "description": "可选项目交付契约的唯一权威路径"
         },
         "bugIntake": {