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/lib/env.ts

@@ -0,0 +1,47 @@
+// Build-time configuration for the Galaxy gateway. Both values arrive
+// through Vite `import.meta.env` and resolve to module-level constants
+// at the first import.
+//
+// `VITE_GATEWAY_BASE_URL` is the base URL of the gateway public REST
+// surface and the Connect-Web authenticated edge (same host, same
+// port; the gateway listener serves both). It defaults to the local
+// dev address used by `tools/local-ci` and the integration suite.
+//
+// `VITE_GATEWAY_RESPONSE_PUBLIC_KEY` is the gateway's response-signing
+// Ed25519 public key, encoded as standard (non-URL-safe) base64 of
+// the raw 32-byte key. Decoded once on module load and exported as
+// `Uint8Array`. The value is only consumed by [GalaxyClient] when a
+// signed unary call is dispatched; the unauthenticated routes do not
+// need it. An empty or malformed value therefore does not block app
+// boot — it surfaces only when the lobby route opens its first
+// authenticated call.
+
+const RAW_BASE_URL: string =
+	(import.meta.env.VITE_GATEWAY_BASE_URL as string | undefined) ??
+	"http://localhost:8080";
+
+const RAW_RESPONSE_PUBLIC_KEY: string =
+	(import.meta.env.VITE_GATEWAY_RESPONSE_PUBLIC_KEY as string | undefined) ??
+	"";
+
+export const GATEWAY_BASE_URL: string = stripTrailingSlash(RAW_BASE_URL);
+
+export const GATEWAY_RESPONSE_PUBLIC_KEY: Uint8Array = decodeBase64(
+	RAW_RESPONSE_PUBLIC_KEY,
+);
+
+function stripTrailingSlash(url: string): string {
+	return url.endsWith("/") ? url.slice(0, -1) : url;
+}
+
+function decodeBase64(value: string): Uint8Array {
+	if (value.length === 0) {
+		return new Uint8Array();
+	}
+	const binary = atob(value);
+	const bytes = new Uint8Array(binary.length);
+	for (let i = 0; i < binary.length; i++) {
+		bytes[i] = binary.charCodeAt(i);
+	}
+	return bytes;
+}