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/stores/message-v2/normalizers.ts

@@ -1,4 +1,4 @@
-import { decodeHtmlEntities } from "../../lib/markdown"
+import { decodeHtmlEntities } from "../../lib/text-render-utils"
 
 function decodeTextSegment(segment: any): any {
   if (typeof segment === "string") {