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/shared/ui/molecules/async.component.ts

@@ -0,0 +1,32 @@
+import { Component, input, output } from '@angular/core';
+import { SpinnerComponent } from '@shared/ui/atoms/spinner.component';
+import type { RemoteData } from '@shared/application/remote-data';
+
+@Component({
+  selector: 'app-async',
+  imports: [SpinnerComponent],
+  template: `
+    @switch (data().tag) {
+      @case ('Loading') {
+        <app-spinner />
+      }
+      @case ('Empty') {
+        <p>{{ emptyText() }}</p>
+      }
+      @case ('Failure') {
+        <p role="alert">{{ errorText() }}</p>
+        <button type="button" (click)="retry.emit()">{{ retryText() }}</button>
+      }
+      @case ('Success') {
+        <ng-content />
+      }
+    }
+  `,
+})
+export class AsyncComponent<T> {
+  data = input.required<RemoteData<unknown, T>>();
+  emptyText = input('No data.');
+  errorText = input('Something went wrong.');
+  retryText = input('Retry');
+  retry = output<void>();
+}