feat: open subagent sessions read-only in context panel

Adds read-only embedded chat mode without hiding permission prompts
Opens subagent sessions in the context panel instead of replacing the main chat
Fixes context panel message loading for embedded sessions

packages/ui/src/lib/i18n/messages/zh-CN.ts

@@ -1399,6 +1399,7 @@ export const dict: Record<I18nKey, string> = {
   'chat.container.returnToParent.titleNamed': '返回到：{title}',
   'chat.container.returnToParent.title': '返回父会话',
   'chat.container.returnToParent.label': '父级',
+  'chat.container.readOnlySubagentPromptBanner': '无法向子代理会话发送提示。',
   'chat.unifiedControls.title': '控制',
   'chat.unifiedControls.model.title': '模型',
   'chat.unifiedControls.model.noRecent': '没有最近使用的模型',