feat(FN-1685): normalize changeset frontmatter and fix test expectations

- Remove unnecessary name fields from changeset files that reference @fusion/* packages
- Fix experimentalFeatures test expectation to match actual merge behavior
- Update test description to clarify merge vs replace semantics

packages/core/src/store.test.ts

@@ -1210,6 +1210,7 @@ describe("TaskStore", () => {
 
       const settings = await store.getSettings();
       // Note: updateSettings merges experimentalFeatures, preserving existing features
+      // To replace entirely, pass null for experimentalFeatures first, then the new object
       expect(settings.experimentalFeatures).toEqual({ "feature-a": true, "feature-b": true });
     });