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/es/instance.ts

@@ -90,6 +90,7 @@ export const instanceMessages = {
 
   "instanceShell.rightPanel.title": "Panel de estado",
   "instanceShell.rightPanel.tabs.changes": "Cambios",
+  "instanceShell.rightPanel.tabs.gitChanges": "Cambios de Git",
   "instanceShell.rightPanel.tabs.files": "Archivos",
   "instanceShell.rightPanel.tabs.status": "Estado",
   "instanceShell.rightPanel.tabs.ariaLabel": "Pestañas del panel derecho",
@@ -112,6 +113,10 @@ export const instanceMessages = {
   "instanceShell.sessionChanges.filesChanged": "{count} archivos cambiados",
   "instanceShell.sessionChanges.actions.show": "Mostrar cambios",
 
+  "instanceShell.gitChanges.loading": "Cargando cambios de Git...",
+  "instanceShell.gitChanges.empty": "Aún no hay cambios de Git.",
+  "instanceShell.gitChanges.deleted": "Eliminado",
+
   "instanceShell.filesShell.fileListTitle": "Lista de archivos",
   "instanceShell.filesShell.mobileSelectorLabel": "Seleccionar archivo",
   "instanceShell.filesShell.mobileSelectorEmpty": "Selecciona un archivo",