test: enrich coverage for queryKeys, BaseQueryStore, and BatchFontStore

- queryKeys: add mutation-safety test for batch(), key hierarchy tests
  (list/batch/detail keys rooted in their parent base keys), and
  unique-key test for different detail IDs
- BaseQueryStore: add initial-state test (data undefined, isError false
  before any fetch resolves)
- BatchFontStore: add FontResponseError type assertion on malformed
  response, null error assertion on success, and setIds([]) disables
  query and returns empty fonts without triggering a fetch

src/shared/lib/helpers/BaseQueryStore.test.ts

@@ -51,6 +51,12 @@ describe('BaseQueryStore', () => {
             await vi.waitFor(() => expect(store.data).toBe('ok'), { timeout: 1000 });
             expect(store.isLoading).toBe(false);
         });
+
+        it('should have undefined data and no error in initial loading state', () => {
+            const store = new TestStore(['initial-state'], () => new Promise(r => setTimeout(() => r('late'), 500)));
+            expect(store.data).toBeUndefined();
+            expect(store.isError).toBe(false);
+        });
     });
 
     describe('Error Handling', () => {