feat(worker): add logout + replace admin-only settings with Account screen

The Instellingen tab was activity management, which Phase 2 made admin-only —
workers saw add/edit/delete controls that all 403. Replace it with an Account
tab showing the signed-in name/email (via /api/me) and an Uitloggen button
(wires the existing AuthContext signOut). Activity management belongs to the
Phase 3 admin app, so the worker client drops the Settings screen and its
now-unused activity-mutation hooks (useActivities read stays).

Products affected: SoleLog worker client (apps/worker).

apps/worker/src/App.test.tsx

@@ -18,7 +18,7 @@ function renderApp() {
   return render(
     <QueryClientProvider client={queryClient}>
       <App />
-    </QueryClientProvider>,
+    </QueryClientProvider>
   );
 }
 
@@ -40,6 +40,6 @@ describe('App', () => {
     const tabbar = within(screen.getByRole('navigation'));
     expect(tabbar.getByText('Stopwatch')).toBeInTheDocument();
     expect(tabbar.getByText('Geschiedenis')).toBeInTheDocument();
-    expect(tabbar.getByText('Instellingen')).toBeInTheDocument();
+    expect(tabbar.getByText('Account')).toBeInTheDocument();
   });
 });