🧪 fix: stub useAttachmentPreviewSync in pre-existing Attachment test mocks

The new `useAttachmentPreviewSync` hook is called unconditionally inside
`FileAttachment` (added in the prior commit). Two pre-existing test
files mock `~/hooks` to provide `useLocalize` only — the un-mocked
preview hook reference resolved to undefined and crashed render with
`(0 , _hooks.useAttachmentPreviewSync) is not a function` on the
Ubuntu/Windows CI runners.

Fix is local to the test mocks: add a no-op stub that returns
`{ status: 'ready' }` so the component renders the legacy chip path.
The two-phase preview behavior itself has its own dedicated suites
(`useAttachmentHandler.spec.tsx`, `useAttachmentPreviewSync.spec.tsx`).

client/src/components/Chat/Messages/Content/Parts/__tests__/ArtifactRouting.test.tsx

@@ -11,6 +11,11 @@ jest.mock('~/hooks', () => ({
     () =>
     (key: string): string =>
       key,
+  /* `FileAttachment` calls this hook unconditionally to bridge the
+   * two-phase preview lifecycle into the attachment cache. The
+   * routing tests don't exercise the preview flow itself — stub it
+   * to a no-op so it doesn't blow up jsdom rendering. */
+  useAttachmentPreviewSync: () => ({ status: 'ready', previewError: undefined, isPolling: false }),
 }));
 
 jest.mock('../LogLink', () => ({

client/src/components/Chat/Messages/Content/Parts/__tests__/TextAttachment.test.tsx

@@ -13,6 +13,10 @@ jest.mock('~/hooks', () => ({
       };
       return translations[key] ?? key;
     },
+  /* `FileAttachment` calls this hook unconditionally to bridge the
+   * two-phase preview lifecycle. Stub to a no-op for tests that
+   * don't exercise the preview flow. */
+  useAttachmentPreviewSync: () => ({ status: 'ready', previewError: undefined, isPolling: false }),
 }));
 
 const mockHandleDownload = jest.fn();