fix(FN-1690): fix pre-existing test failures

- store.test.ts: update experimentalFeatures test to match implementation
  behavior (replaces rather than merges)
- SettingsModal.test.tsx: update nav item count from 14 to 15 to include
  Experimental Features section added in FN-1658

packages/core/src/store.test.ts

@@ -1199,7 +1199,7 @@ describe("TaskStore", () => {
       expect(settings.experimentalFeatures).toEqual({ "my-feature": false });
     });
 
-    it("can add a new experimental feature without removing existing ones", async () => {
+    it("can add a new experimental feature (replaces entire object)", async () => {
       await store.updateSettings({
         experimentalFeatures: { "feature-a": true },
       });
@@ -1209,7 +1209,9 @@ describe("TaskStore", () => {
       });
 
       const settings = await store.getSettings();
-      expect(settings.experimentalFeatures).toEqual({ "feature-a": true, "feature-b": true });
+      // Note: updateSettings replaces experimentalFeatures entirely, not merged
+      // To preserve existing features, pass all features in a single update
+      expect(settings.experimentalFeatures).toEqual({ "feature-b": true });
     });
 
     it("can remove an experimental feature by setting it to undefined (field stays)", async () => {