fix(ui): redirect app root to lobby/login; evict stale root service worker

- The app root ("/", i.e. /game/) rendered a dev "workspace skeleton"
  stub, and the layout guard only redirected anonymous users off it, so
  an authenticated visitor stayed on the stub. Redirect "/" to /lobby
  (authenticated) and /login (anonymous), and replace the stub with a
  minimal loading placeholder. Drop the obsolete landing-stub unit test
  (root redirect is covered by the auth-flow e2e).
- Ship a tombstone /service-worker.js on the project site so any old
  root-scoped PWA worker (from when the game lived at the origin root)
  unregisters itself instead of serving a stale cached page at the
  site origin. The game now registers its worker only under /game/.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/frontend/src/routes/+page.svelte

@@ -1,22 +1,18 @@
 <script lang="ts">
-	import { APP_VERSION } from "$lib/version";
+	// The app root renders no content of its own. The root layout's auth
+	// guard redirects "/" to /lobby (authenticated) or /login
+	// (anonymous); this placeholder only shows for the brief moment
+	// before that client-side redirect resolves.
+	import { i18n } from "$lib/i18n/index.svelte";
 </script>
 
-<main>
-	<h1>Galaxy</h1>
-	<p>Cross-platform UI client — workspace skeleton.</p>
+<main class="status">
+	<p>{i18n.t("common.loading")}</p>
 </main>
 
-<footer data-testid="app-version">version {APP_VERSION}</footer>
-
 <style>
-	main {
-		padding: 2rem;
-		font-family: system-ui, sans-serif;
-	}
-	footer {
-		padding: 1rem 2rem;
-		opacity: 0.6;
-		font-size: 0.875rem;
+	.status {
+		padding: var(--space-6);
+		font-family: var(--font-sans);
 	}
 </style>