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/users.page.ts

@@ -0,0 +1,31 @@
+import { Component, computed, signal } from '@angular/core';
+import { PageShellComponent } from '@shared/ui/templates/page-shell.component';
+import { AsyncComponent } from '@shared/ui/molecules/async.component';
+import { fromResource } from '@shared/application/remote-data';
+import { UserListComponent } from '@users/ui/organisms/user-list.component';
+import { UserDetailComponent } from '@users/ui/organisms/user-detail.component';
+import { usersResource } from '@users/application/users.resource';
+import { isEmptyUserList } from '@users/domain/user';
+
+@Component({
+  selector: 'app-users-page',
+  imports: [PageShellComponent, AsyncComponent, UserListComponent, UserDetailComponent],
+  template: `
+    <app-page-shell heading="Users">
+      @if (selectedUserId(); as id) {
+        <app-user-detail [userId]="id" (close)="selectedUserId.set(null)" />
+      } @else {
+        <app-async [data]="listData()" (retry)="usersResource.reload()">
+          @if (usersResource.hasValue()) {
+            <app-user-list [users]="usersResource.value()!" (select)="selectedUserId.set($event)" />
+          }
+        </app-async>
+      }
+    </app-page-shell>
+  `,
+})
+export class UsersPage {
+  protected selectedUserId = signal<number | null>(null);
+  protected usersResource = usersResource();
+  protected listData = computed(() => fromResource(this.usersResource, isEmptyUserList));
+}