feat(spa): scaffold Angular app shell with host/player routes

frontend/angular/src/app/app.component.html

@@ -0,0 +1,13 @@
+<main class="shell">
+  <header class="shell__header">
+    <h1>WPP Angular Shell</h1>
+    <nav>
+      <a routerLink="/host">Host</a>
+      <a routerLink="/player">Player</a>
+    </nav>
+  </header>
+
+  <section class="shell__content">
+    <router-outlet></router-outlet>
+  </section>
+</main>