perf: reduce streaming render cost and refresh activity page on demand

- Segment streaming Markdown so completed blocks are reused and only the growing tail is re-parsed; fall back to whole-document parsing for document-wide constructs
- Memoize conversation sidebar rows and cache per-conversation derived activity, ordering and pending approvals
- Activity page loads on entry, refreshes every 15 s while visible, and has a single header refresh button
- Include pending settings, model download source, device sharing and knowledge gateway changes in the working tree
- Add Electron streaming input benchmark and regression tests

docs/features/application-tool-navigation/progress.md

@@ -2,8 +2,9 @@
 
 ## 2026-10-01：设备共享入口
 
-新增 `device-sharing`，应用菜单及管理 Modal 均进入主内容区页面；管理行可排序，不提供启用
-或常驻开关。旧顺序通过现有存储归一化追加新项，保留原设置；权威写入要求五项完整顺序。
+新增 `device-sharing`，启用后应用菜单及管理 Modal 均进入主内容区页面；管理行可排序。
+首期初始实现没有启用开关，同日后续改为测试阶段默认关闭、可手动启用，不提供常驻开关。
+旧顺序通过现有存储归一化追加新项，保留原设置；权威写入要求五项完整顺序。
 ApplicationCenter、ApplicationMenu、设置迁移以及 App 入口／排序回归已通过，真实 Electron
 从应用中心进入页面并完成后端流程。精确命令、完整范围及全仓测试记录见
 [设备共享实施进度](../device-sharing/progress.md)。下方历史四应用记录保留原验证时的范围。