feat(client): configure host-plane plugins from a settings section

The section knows no namespace: it declares `settings.plugin.item` and
renders whatever cards were registered into it, so a plugin that ships a
browser half owns its card and its controls. The three cards here cover the
host-plane sections this deployment exposes.

A field shows its effective value and, when the raw user layer carries it, an
override badge and a reset that clears it back to the composition layer.
Controls commit on blur and Enter rather than per keystroke, which would burn
namespace revisions and race its own reads. The search key is the one value
that never rides a response: the card reports only whether one is configured
and writes it through the credentials domain, addressed by the reference the
section names.

A card renders nothing while its namespace is unavailable — a deployment that
does not compose the owning plugin should show no trace of it rather than a
disabled card the user cannot act on.

packages/client/README.zh.md

@@ -32,6 +32,7 @@ dsh web GUI 的浏览器侧：shell 启动、浏览器与宿主通信、共享 U
 | [`ui-model/`](ui-model/README.md) | 在会话界面中提供模型选择。 |
 | [`ui-permission/`](ui-permission/README.md) | 配置默认权限并切换当前会话的访问模式。 |
 | [`ui-plan/`](ui-plan/README.md) | 展示生效中的 plan mode 状态及其退出控件。 |
+| [`ui-plugin-config/`](ui-plugin-config/README.md) | 插件设置分区：把宿主平面的插件配置呈现为可展开卡片。 |
 | [`ui-question/`](ui-question/README.md) | 展示 agent 请求的交互式问题。 |
 | [`ui-agent-preset/`](ui-agent-preset/README.md) | 选择会话的 agent 预设，并创作预设组装。 |
 | [`ui-settings/`](ui-settings/README.md) | 承载设置界面及其扩展区域。 |