feat(web): draft a custom preset in a creator-mode session

The settings section gains the conversational authoring entry beside
copying: a dashed add-card (the Models page's affordance) that stages the
self-referential cordis preset and starts a new session on it, closing the
settings panel through the shell's new section owner-prop `close` — the
one shell affordance a section receives, for flows that leave settings.

The seat learns the difference between picking and staging: `select()`'s
immediate apply meets the still-current running session and drops the
stage as unservable, so the entry uses `stage()` and leaves the apply to
the list-change applier that fires when the started session becomes
current. `load()` stops regressing the display when its reply lands after
an applied stage was consumed — staged pick first, then the composition
the current session already carries, then the deployment default.

The authoring lane connects a workspace and drives the gesture to a
composed host session; the section goldens gain the entry.

packages/client/ui-agent-preset/README.zh.md

@@ -36,6 +36,8 @@ chip 以部署默认值打开，其选择是**暂存**的——该界面先于
 
 随附 preset 在只读查看器中打开。它是副本据以出发的已知良好组装，因此能读到它正是意义所在；它不提供位置也不提供删除——它的安装目录会被升级覆盖，不归用户管理。开篇引导语承担了从前创建按钮所暗示的信息：想从最小的骨架开始，就复制极简模式（31 行，对照 standard 的 233 行）。
 
+复制旁边是对话式入口：名单携带自指的 `cordis` preset 时，一张虚线添加卡（模型页的同款样式）会暂存它并开启新会话——分区经外壳的 owner-prop `close` 关闭设置面板，新会话 chip 自己的应用器负责组装工作区流程产出的空白会话。seat 会防止晚到的名单加载回退显示：暂存选择优先，其次是当前会话已携带的组装，最后才是部署默认值。
+
 对话框复刻宿主自身的约束规则（`[a-z0-9][a-z0-9-]*`），并拒绝已被占用的名称——复制从不覆写。这两项检查只是便利：宿主会重新校验，失败时对话框报告的正是宿主的答复。
 
 删除会移除整个 preset 目录。已据其组装的会话继续运行——组装在会话创建时挂载一次，此后没有任何东西会重新读取该文件。