fix(test): resolve unhandled rejection in sidebar logout error test

The 'should handle logout errors gracefully' test mocked supabase.auth.signOut
to reject (throw), which does not match real supabase-js behaviour (signOut
resolves with { error }, never throws). The rejecting mock caused an unhandled
promise rejection in the async handleLogout onClick handler: tolerated locally
(vitest exit 0) but failing in CI (npx vitest run exits 1).

Switch to a realistic resolved-with-error mock and assert the user is still
redirected to /login (true graceful handling). No production code change.

admin-web/components/sidebar.test.tsx

@@ -91,8 +91,10 @@ describe('Sidebar', () => {
   })
 
   it('should handle logout errors gracefully', async () => {
-    mockSignOut.mockRejectedValueOnce(new Error('Network error'))
-    
+    // Real supabase.auth.signOut() never throws — it resolves with { error }.
+    // Mocking it realistically avoids an unhandled rejection and matches prod behaviour.
+    mockSignOut.mockResolvedValueOnce({ error: new Error('Network error') })
+
     render(<Sidebar />)
 
     const logoutButton = screen.getByRole('button', { name: /logout/i })
@@ -101,6 +103,9 @@ describe('Sidebar', () => {
     await waitFor(() => {
       expect(mockSignOut).toHaveBeenCalled()
     })
+
+    // Graceful: even when signOut errors, the user is still redirected to login.
+    expect(mockPush).toHaveBeenCalledWith('/login')
   })
 
   it('should have correct styling for navigation', () => {