perf(ui): lazy-load markdown and defer diff rendering (#215)

## Summary
- lazy-load the markdown and diff render paths so they stop inflating
initial UI startup work
- move shared text rendering helpers out of the markdown path and keep
diff rendering on the deferred path
- defer the Monaco secondary viewers so the markdown and diff path no
longer keeps that work in the main bundle

## Follow-ups
- related fork follow-up: Pagecran/CodeNomad#1
- that follow-up is now independent on dev and only keeps the remaining
right panel, picker, and tool-call secondary chunking work

## Testing
- npm run typecheck --workspace @codenomad/ui
- npm run build --workspace @codenomad/ui

packages/ui/src/lib/i18n/messages/zh-Hans/instance.ts

@@ -90,6 +90,7 @@ export const instanceMessages = {
 
   "instanceShell.rightPanel.title": "状态面板",
   "instanceShell.rightPanel.tabs.changes": "更改",
+  "instanceShell.rightPanel.tabs.gitChanges": "Git 更改",
   "instanceShell.rightPanel.tabs.files": "文件",
   "instanceShell.rightPanel.tabs.status": "状态",
   "instanceShell.rightPanel.tabs.ariaLabel": "右侧面板标签页",
@@ -112,6 +113,10 @@ export const instanceMessages = {
   "instanceShell.sessionChanges.filesChanged": "已更改 {count} 个文件",
   "instanceShell.sessionChanges.actions.show": "显示更改",
 
+  "instanceShell.gitChanges.loading": "正在加载 Git 更改...",
+  "instanceShell.gitChanges.empty": "暂无 Git 更改。",
+  "instanceShell.gitChanges.deleted": "已删除",
+
   "instanceShell.filesShell.fileListTitle": "文件列表",
   "instanceShell.filesShell.mobileSelectorLabel": "选择文件",
   "instanceShell.filesShell.mobileSelectorEmpty": "请选择文件",