…llisions

When multiple share scopes exist on the same page (e.g., react-18 and
react-19 for cross-major React isolation via bridge components), the
loadShare flat cache key ignores the scope. Whichever scope populates
the cache first wins — all subsequent lookups return the wrong version.

Prefix cache keys with `shareItem.scope:` (defaults to "default:") so
scoped singletons like react-18:react and react-19:react don't collide.
Also emit a runtime helper (__mfGetSharedCacheKey) for the three inline
cache-key sites in virtualRemoteEntry that can't call the build-time
getSharedCacheKey().

Co-Authored-By: Claude Opus 4.6 <[email protected]>