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/ru/instance.ts

@@ -90,6 +90,7 @@ export const instanceMessages = {
 
   "instanceShell.rightPanel.title": "Панель состояния",
   "instanceShell.rightPanel.tabs.changes": "Изменения",
+  "instanceShell.rightPanel.tabs.gitChanges": "Изменения Git",
   "instanceShell.rightPanel.tabs.files": "Файлы",
   "instanceShell.rightPanel.tabs.status": "Статус",
   "instanceShell.rightPanel.tabs.ariaLabel": "Вкладки правой панели",
@@ -112,6 +113,10 @@ export const instanceMessages = {
   "instanceShell.sessionChanges.filesChanged": "Изменено файлов: {count}",
   "instanceShell.sessionChanges.actions.show": "Показать изменения",
 
+  "instanceShell.gitChanges.loading": "Загрузка изменений Git...",
+  "instanceShell.gitChanges.empty": "Изменений Git пока нет.",
+  "instanceShell.gitChanges.deleted": "Удалено",
+
   "instanceShell.filesShell.fileListTitle": "Список файлов",
   "instanceShell.filesShell.mobileSelectorLabel": "Выбрать файл",
   "instanceShell.filesShell.mobileSelectorEmpty": "Выберите файл",