feat: minimal signals + RemoteData template with a users feature

Extracted from atomic-design-poc: RemoteData<E,T> (bare union + fromResource,
no combinators) + a trimmed <app-async> switch, no Elm-style store — state is
resource() plus one plain signal. Minimal DDD layering per context
(domain/infrastructure/application/ui) combined with atomic design inside
ui/ (atoms/molecules/organisms/templates/pages), mirroring the POC's
conventions at template scale.

One worked feature (users/): a list with a click-through to a detail view
(its own independent resource() fetch) and a Back action. Tests are
BDD-style (describe/it, one assertion per it) and black-box (assert
rendered DOM/emitted events only) - 100% branch/line coverage. README.md
documents what's deliberately omitted vs. the POC and the concrete growth
path back to it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/users/ui/organisms/user-detail.component.spec.ts

@@ -0,0 +1,42 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { TestBed } from '@angular/core/testing';
+import { UserDetailComponent } from './user-detail.component';
+
+afterEach(() => {
+  vi.unstubAllGlobals();
+});
+
+describe('UserDetailComponent', () => {
+  it("shows the fetched user's name and email once resolved", async () => {
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockResolvedValue({
+        json: () => Promise.resolve({ id: 1, name: 'Ada', email: 'ada@example.com' }),
+      }),
+    );
+    await TestBed.configureTestingModule({ imports: [UserDetailComponent] }).compileComponents();
+    const fixture = TestBed.createComponent(UserDetailComponent);
+    fixture.componentRef.setInput('userId', 1);
+    fixture.detectChanges();
+    await fixture.whenStable();
+    fixture.detectChanges();
+    expect(fixture.nativeElement.textContent).toContain('ada@example.com');
+  });
+
+  it('emits close when the back button is clicked', async () => {
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockResolvedValue({
+        json: () => Promise.resolve({ id: 1, name: 'Ada', email: 'a@x.com' }),
+      }),
+    );
+    await TestBed.configureTestingModule({ imports: [UserDetailComponent] }).compileComponents();
+    const fixture = TestBed.createComponent(UserDetailComponent);
+    fixture.componentRef.setInput('userId', 1);
+    fixture.detectChanges();
+    let closed = false;
+    fixture.componentInstance.close.subscribe(() => (closed = true));
+    fixture.nativeElement.querySelectorAll('button')[0].click();
+    expect(closed).toBe(true);
+  });
+});