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/app.ts

@@ -1,11 +1,10 @@
-import { Component, signal } from '@angular/core';
+import { Component } from '@angular/core';
+import { UsersPage } from '@users/ui/users.page';
 
 @Component({
   selector: 'app-root',
-  imports: [],
+  imports: [UsersPage],
   templateUrl: './app.html',
-  styleUrl: './app.css'
+  styleUrl: './app.css',
 })
-export class App {
-  protected readonly title = signal('ng-signals-template');
-}
+export class App {}