test(web): cover the plugin configuration section end to end

Three scenarios over the real wire: the cards this deployment's exposed
namespaces produce, one field edited down to the settings document with the
override badge that layering produces, and the reset that clears it back to
the composed default.

Every other settings golden gains the same nav entry and nothing else.

apps/web/tests/snapshots/models-settings/declared.expected.md

@@ -10,6 +10,9 @@
     - button "Agent 预设":
       - img
       - text: Agent 预设
+    - button "插件":
+      - img
+      - text: 插件
   - button "打开配置文件"
   - button "关闭":
     - img