feat(site): add POST /site/cookie/{site_id} endpoint for updating site Cookie&UA via request body

- Introduce SiteCookieUpdate schema for structured cookie update requests
- Add POST endpoint to update site Cookie&UA using JSON body
- Refactor cookie update logic into shared _update_site_cookie function
- Update SKILL.md to document new endpoint and endpoint count
- Add tests for both POST and legacy GET cookie update endpoints

tests/test_site_cookie_endpoint.py

@@ -0,0 +1,64 @@
+from types import SimpleNamespace
+from unittest.mock import Mock, patch
+
+from app import schemas
+from app.api.endpoints import site as site_endpoint
+
+
+def test_update_cookie_by_body_uses_request_body():
+    """
+    POST 更新站点 Cookie 时应从请求体读取登录参数。
+    """
+    fake_site = SimpleNamespace(id=1, name="TestSite")
+    fake_chain = Mock()
+    fake_chain.update_cookie.return_value = (True, "ok")
+    request = schemas.SiteCookieUpdate(username="user", password="password", code="123456")
+
+    with patch.object(site_endpoint.Site, "get", return_value=fake_site), patch.object(
+        site_endpoint, "SiteChain", return_value=fake_chain
+    ):
+        response = site_endpoint.update_cookie_by_body(
+            site_id=1,
+            site_cookie_update=request,
+            db=Mock(),
+            _=Mock(),
+        )
+
+    assert response.success is True
+    assert response.message == "ok"
+    fake_chain.update_cookie.assert_called_once_with(
+        site_info=fake_site,
+        username="user",
+        password="password",
+        two_step_code="123456",
+    )
+
+
+def test_update_cookie_legacy_get_keeps_query_params():
+    """
+    旧 GET 入口仍应兼容查询参数更新站点 Cookie。
+    """
+    fake_site = SimpleNamespace(id=1, name="TestSite")
+    fake_chain = Mock()
+    fake_chain.update_cookie.return_value = (False, "failed")
+
+    with patch.object(site_endpoint.Site, "get", return_value=fake_site), patch.object(
+        site_endpoint, "SiteChain", return_value=fake_chain
+    ):
+        response = site_endpoint.update_cookie(
+            site_id=1,
+            username="user",
+            password="password",
+            code=None,
+            db=Mock(),
+            _=Mock(),
+        )
+
+    assert response.success is False
+    assert response.message == "failed"
+    fake_chain.update_cookie.assert_called_once_with(
+        site_info=fake_site,
+        username="user",
+        password="password",
+        two_step_code=None,
+    )