Spike: modular React studio loading UI modules from NuGet packages #8839

Part of the React studio preview (3.11) epic.

Size: M (~3 working days)
Depends on: none

Goal

Prove the module architecture before the port: an ASP.NET Core host + SDK v0 (routes, navigation, UI-hint editor slots) + import map, an in-box Labels module and a third-party sample module consumed only as a .nupkg from a local feed.

Acceptance criteria

• Both modules load from packed .nupkg files; the third-party one has no project reference to the host
• Exactly one React instance at runtime (shared context such as query client and theme works across modules)
• The manifest endpoint lists only modules whose CShells feature is enabled
• A module with an incompatible host/SDK major is rejected with a visible diagnostic; the shell still works
• Asset URLs carry the package version (cache-busting)
• Vite HMR dev loop works through the host; a CSP with a nonce works with the import map
• A Playwright smoke test passes; go/no-go is recorded in the ADR