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_knowledge.py

@@ -189,10 +189,10 @@ def _timestamp(value: Any) -> datetime | None:
 
 
 def infer_project_root(document_path: Path) -> Path | None:
-    """从标准 docs/ack 布局或 Git marker 推断项目根，不解析文档 symlink。"""
+    """从标准 .pouch/ack 布局或 Git marker 推断项目根，不解析文档 symlink。"""
     lexical = document_path.expanduser().absolute()
     parent = lexical.parent
-    if parent.name == "ack" and parent.parent.name == "docs":
+    if parent.name == "ack" and parent.parent.name in {".pouch", "docs"}:
         return parent.parent.parent.resolve()
     for candidate in (parent, *parent.parents):
         if (candidate / ".git").exists():
@@ -245,7 +245,7 @@ def _tasks_project_root(
         return inferred
 
     # Legacy task boards may still declare repoPath. It is only a fallback for
-    # non-standard layouts; docs/ack location is authoritative when available.
+    # non-standard layouts; .pouch/ack location is authoritative when available.
     project = tasks_data.get("project")
     repo_path = project.get("repoPath") if isinstance(project, dict) else None
     if _nonempty(repo_path):
@@ -779,10 +779,10 @@ def _validate_knowledge_file_binding(
     knowledge_file = project.get("knowledgeFile")
     if not _nonempty(knowledge_file):
         return ["[tasks] project.knowledgeFile 必填"]
-    if knowledge_file != "docs/ack/knowledge.yaml":
+    if knowledge_file != ".pouch/ack/knowledge.yaml":
         errors.append(
             "[tasks] project.knowledgeFile 必须固定为 "
-            "'docs/ack/knowledge.yaml'"
+            "'.pouch/ack/knowledge.yaml'"
         )
     relative = Path(knowledge_file)
     segments = knowledge_file.replace("\\", "/").split("/")
@@ -812,7 +812,7 @@ def _validate_knowledge_file_binding(
     binding_root = project_root or declared_root
     if binding_root is None or not binding_root.is_dir():
         errors.append(
-            "[tasks] 无法从 docs/ack 布局确定现有项目根目录；"
+            "[tasks] 无法从 .pouch/ack 布局确定现有项目根目录；"
             "请传入 --project-root"
         )
         return errors
@@ -1071,7 +1071,7 @@ def main(argv: list[str] | None = None) -> int:
     parser.add_argument("--tasks", help="可选 tasks.yaml，用于跨文件引用校验")
     parser.add_argument(
         "--project-root",
-        help="可选项目根目录；默认从 tasks.yaml 的 docs/ack 布局推断",
+        help="可选项目根目录；默认从 tasks.yaml 的 .pouch/ack 布局推断",
     )
     args = parser.parse_args(argv)