refactor(delete): make undo unconditional, remove undo toggle and button delay

- Remove delete_undo_enabled setting (backend default, frontend state,
  settings modal UI, 10 locales); staged deletes with 30s undo are now
  the only delete path and stale settings keys are silently ignored
- Remove the 1500ms delete-button arm delay (armDeleteButton) from all
  delete modals; misclicks are recoverable via the undo toast
- Delete modal always shows the recoverable warning
- Log the first staged file path in staging log lines for easier support

tests/frontend/managers/BulkManager.bulkDelete.test.js

@@ -332,41 +332,3 @@ describe('BulkManager.confirmBulkDelete undo flows', () => {
     expect(resetAndReloadMock).not.toHaveBeenCalled();
   });
 });
-
-describe('BulkManager.showBulkDeleteModal delay-activate', () => {
-  beforeEach(() => {
-    vi.useFakeTimers();
-    stateStub.currentPageType = 'loras';
-    stateStub.selectedModels.clear();
-    stateStub.selectedModels.add('/models/a.safetensors');
-    document.body.innerHTML = `
-      <div id="bulkDeleteModal" class="modal delete-modal">
-        <h2></h2>
-        <p class="delete-message"></p>
-        <div class="delete-model-info"><p></p></div>
-        <button class="cancel-btn">Cancel</button>
-        <button class="delete-btn">Delete</button>
-      </div>
-    `;
-  });
-
-  afterEach(() => {
-    vi.useRealTimers();
-    document.body.innerHTML = '';
-  });
-
-  it('opens with the delete button disabled and enables it after 1500ms', async () => {
-    const { BulkManager } = await import('../../../static/js/managers/BulkManager.js');
-    const bulk = new BulkManager();
-    bulk.showBulkDeleteModal();
-
-    const deleteBtn = document.querySelector('#bulkDeleteModal .delete-btn');
-    expect(deleteBtn.disabled).toBe(true);
-
-    deleteBtn.click();
-    expect(bulkDeleteModelsMock).not.toHaveBeenCalled();
-
-    vi.advanceTimersByTime(1500);
-    expect(deleteBtn.disabled).toBe(false);
-  });
-});