Feat: Add Copy URL button and reusable toast notification system

Detail page now has a "Copy URL" button that copies the image's direct
file URL to the clipboard. A toast service (BehaviorSubject-backed,
auto-dismissing after 3s) confirms success or failure. ToastComponent
is registered at the app root and available to all future features.

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

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

@@ -0,0 +1,49 @@
+import { TestBed } from '@angular/core/testing';
+import { of } from 'rxjs';
+import { ToastComponent } from './toast.component';
+import { ToastService } from '../services/toast.service';
+
+describe('ToastComponent', () => {
+  let toastSvc: jasmine.SpyObj<ToastService>;
+
+  beforeEach(async () => {
+    toastSvc = jasmine.createSpyObj('ToastService', [], { current$: of(null) });
+
+    await TestBed.configureTestingModule({
+      imports: [ToastComponent],
+      providers: [{ provide: ToastService, useValue: toastSvc }],
+    }).compileComponents();
+  });
+
+  it('renders a .toast element with the correct message when current$ emits a toast', async () => {
+    Object.defineProperty(toastSvc, 'current$', { value: of({ message: 'Done', type: 'success' as const }) });
+    const fixture = TestBed.createComponent(ToastComponent);
+    fixture.detectChanges();
+    const el = (fixture.nativeElement as HTMLElement).querySelector('.toast');
+    expect(el).not.toBeNull();
+    expect(el?.textContent?.trim()).toBe('Done');
+  });
+
+  it('adds the success CSS class when type is success', async () => {
+    Object.defineProperty(toastSvc, 'current$', { value: of({ message: 'OK', type: 'success' as const }) });
+    const fixture = TestBed.createComponent(ToastComponent);
+    fixture.detectChanges();
+    const el = (fixture.nativeElement as HTMLElement).querySelector('.toast');
+    expect(el?.classList.contains('success')).toBeTrue();
+  });
+
+  it('adds the error CSS class when type is error', async () => {
+    Object.defineProperty(toastSvc, 'current$', { value: of({ message: 'Fail', type: 'error' as const }) });
+    const fixture = TestBed.createComponent(ToastComponent);
+    fixture.detectChanges();
+    const el = (fixture.nativeElement as HTMLElement).querySelector('.toast');
+    expect(el?.classList.contains('error')).toBeTrue();
+  });
+
+  it('renders nothing when current$ emits null', () => {
+    const fixture = TestBed.createComponent(ToastComponent);
+    fixture.detectChanges();
+    const el = (fixture.nativeElement as HTMLElement).querySelector('.toast');
+    expect(el).toBeNull();
+  });
+});