Fix: Clean up lint errors introduced in test fixes

- Remove unused NEVER import from detail.component.spec.ts
- Replace `null as unknown as ImageRecord` with `null as unknown as typeof MOCK_IMAGE`
  to match the narrower inferred type (thumbnail_key: null) that setup() expects

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/app/detail/detail.component.spec.ts

@@ -2,7 +2,7 @@ import { TestBed } from '@angular/core/testing';
 import { ActivatedRoute, provideRouter, Router } from '@angular/router';
 import { provideHttpClient } from '@angular/common/http';
 import { provideHttpClientTesting } from '@angular/common/http/testing';
-import { of, throwError, Subject, NEVER } from 'rxjs';
+import { of, throwError, Subject } from 'rxjs';
 import { DetailComponent } from './detail.component';
 import { ImageService } from '../services/image.service';
 import { ToastService } from '../services/toast.service';
@@ -114,7 +114,7 @@ describe('DetailComponent', () => {
 
   it('not-found card shown when image is null, loading is false, error is false', () => {
     // Service returns null → fetchImage sets image=null, loading=false, markForCheck()
-    const { fixture } = setup('img-1', of(null as any));
+    const { fixture } = setup('img-1', of(null as unknown as typeof MOCK_IMAGE));
     expect((fixture.nativeElement as HTMLElement).querySelector('.not-found-card')).not.toBeNull();
   });