Slideshow Management Fixes - Convert remaining window.confirm overrides to vi.spyOn.

Follow-up to Copilot review feedback on PR #23: the previous commit added
afterEach(() => vi.restoreAllMocks()) to the Slideshows and SlideshowDetail
test suites, but each file still had one pre-existing test mocking
window.confirm by direct assignment, which vi.restoreAllMocks() does not
restore. If such a test failed before its manual cleanup line, the mock
could leak into later tests and make the suites order-dependent.

Convert those two remaining tests ('handles delete slideshow' and 'handles
delete item') to vi.spyOn(window, 'confirm').mockReturnValue(true) and drop
their manual save/restore, so every window.confirm/window.prompt mock in
both suites is now a spy covered by the afterEach restore.

Full frontend suite passes (137 passed); type-check and lint clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jantman

frontend/src/test/SlideshowDetail.test.tsx

@@ -204,9 +204,8 @@ describe('SlideshowDetail', () => {
       .mockResolvedValueOnce({ success: true, data: mockSlideshow })
       .mockResolvedValueOnce({ success: true, data: mockItems.slice(1) });
 
-    // Mock window.confirm
-    const originalConfirm = window.confirm;
-    window.confirm = vi.fn(() => true);
+    // Spy on window.confirm; restored by afterEach even if the test fails
+    const confirmSpy = vi.spyOn(window, 'confirm').mockReturnValue(true);
 
     render(
       <TestWrapper>
@@ -222,14 +221,11 @@ describe('SlideshowDetail', () => {
     const deleteButtons = screen.getAllByTitle('Delete');
     fireEvent.click(deleteButtons[0]);
 
-    expect(window.confirm).toHaveBeenCalledWith('Are you sure you want to delete "Test Image"?');
+    expect(confirmSpy).toHaveBeenCalledWith('Are you sure you want to delete "Test Image"?');
 
     await waitFor(() => {
       expect(mockApiCall).toHaveBeenCalledWith('/api/v1/slideshow-items/1', { method: 'DELETE' });
     });
-
-    // Cleanup
-    window.confirm = originalConfirm;
   });
 
   it('handles delete of inactive item with permanent-delete confirmation', async () => {

frontend/src/test/Slideshows.test.tsx

@@ -143,9 +143,8 @@ describe('Slideshows', () => {
       .mockResolvedValueOnce({ success: true })
       .mockResolvedValueOnce({ success: true, data: mockSlideshows.slice(1) });
 
-    // Mock window.confirm
-    const originalConfirm = window.confirm;
-    window.confirm = vi.fn(() => true);
+    // Spy on window.confirm; restored by afterEach even if the test fails
+    const confirmSpy = vi.spyOn(window, 'confirm').mockReturnValue(true);
 
     render(
       <TestWrapper>
@@ -161,14 +160,11 @@ describe('Slideshows', () => {
     const deleteButtons = screen.getAllByTitle('Delete');
     fireEvent.click(deleteButtons[0]);
 
-    expect(window.confirm).toHaveBeenCalledWith('Are you sure you want to delete the slideshow "Test Slideshow 1"?');
+    expect(confirmSpy).toHaveBeenCalledWith('Are you sure you want to delete the slideshow "Test Slideshow 1"?');
 
     await waitFor(() => {
       expect(mockApiCall).toHaveBeenCalledWith('/api/v1/slideshows/1', { method: 'DELETE' });
     });
-
-    // Cleanup
-    window.confirm = originalConfirm;
   });
 
   it('handles duplicate slideshow', async () => {