phase 7: auth flow UI (email-code login + session resume + revocation)

Implements ui/PLAN.md Phase 7 end-to-end:

- /login two-step form (email -> code) over the gateway public REST
  surface; /lobby placeholder issues the first authenticated
  user.account.get and renders the decoded display name.
- SessionStore (Svelte 5 runes) with loading / unsupported / anonymous /
  authenticated states; layout-level route guard, browser-not-supported
  blocker, and a minimal SubscribeEvents revocation watcher that closes
  the active client within 1s on a clean stream end or
  Unauthenticated.
- VITE_GATEWAY_BASE_URL + VITE_GATEWAY_RESPONSE_PUBLIC_KEY config plus
  AuthError taxonomy in api/auth.ts.
- Vitest (auth-api, session-store, login-page) and Playwright e2e
  (auth-flow.spec.ts) on the four configured projects, with a fixture
  Ed25519 keypair forging Connect-Web JSON responses.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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

@@ -1,5 +1,70 @@
 <script lang="ts">
+	import { onMount } from "svelte";
+	import { goto } from "$app/navigation";
+	import { page } from "$app/state";
+	import { session } from "$lib/session-store.svelte";
+	import { startRevocationWatcher } from "$lib/revocation-watcher";
+
 	let { children } = $props();
+
+	let stopWatcher: (() => void) | null = null;
+
+	onMount(() => {
+		void session.init();
+		return () => {
+			if (stopWatcher !== null) {
+				stopWatcher();
+				stopWatcher = null;
+			}
+		};
+	});
+
+	$effect(() => {
+		if (session.status === "authenticated" && stopWatcher === null) {
+			stopWatcher = startRevocationWatcher();
+		} else if (session.status !== "authenticated" && stopWatcher !== null) {
+			stopWatcher();
+			stopWatcher = null;
+		}
+
+		const pathname = page.url.pathname;
+		// Debug-only routes under /__debug/* run their own bootstrap
+		// path against the storage primitives and must bypass the
+		// auth guard so Phase 6's Playwright spec can drive the
+		// keystore directly.
+		if (pathname.startsWith("/__debug/")) {
+			return;
+		}
+		if (session.status === "anonymous" && pathname !== "/login") {
+			void goto("/login", { replaceState: true });
+		} else if (session.status === "authenticated" && pathname === "/login") {
+			void goto("/lobby", { replaceState: true });
+		}
+	});
 </script>
 
-{@render children()}
+{#if session.status === "loading"}
+	<main class="status">
+		<p>loading…</p>
+	</main>
+{:else if session.status === "unsupported"}
+	<main class="status">
+		<h1>browser not supported</h1>
+		<p>
+			Galaxy requires Ed25519 in WebCrypto. The minimum supported browser
+			versions are listed in the
+			<a href="https://github.com/galaxy/galaxy/blob/main/ui/docs/storage.md"
+				>storage topic doc</a
+			>.
+		</p>
+	</main>
+{:else}
+	{@render children()}
+{/if}
+
+<style>
+	.status {
+		padding: 2rem;
+		font-family: system-ui, sans-serif;
+	}
+</style>