feat(ui): lobby site-style sidebar + profile screen (#47)

- Wrap lobby and profile in a shared `lobby-shell.svelte` chrome:
  page-list sidebar (Overview/Profile) and a top "Player-xxxx"
  identity strip mirroring the project site's monospace look.
- Strip the legacy `lobby.title`, device-session-id `<code>`, and
  `lobby.greeting` paragraph; the identity strip both names the user
  and opens the profile editor.
- Add a top-level `profile` AppScreen with a three-field form
  (`display_name`, `preferred_language`, `time_zone`) backed by a new
  `src/api/account.ts` wrapper around `user.account.get`,
  `user.profile.update`, and `user.settings.update`. Saving switches
  the active i18n locale in-place when the new preferred language is
  one the UI ships translations for.
- Update e2e fixture + auth-flow / lobby-flow specs to use the new
  `lobby-account-name` testid and wait for the loaded identity before
  releasing pending `SubscribeEvents` (webkit revocation race). New
  `profile-screen.spec.ts` covers navigation, edit-save, and cancel.
- Sync `ui/docs/lobby.md` and `ui/docs/navigation.md` to the new
  layout.

Closes #47

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

@@ -19,6 +19,7 @@
 	import LoginScreen from "$lib/screens/login-screen.svelte";
 	import LobbyScreen from "$lib/screens/lobby-screen.svelte";
 	import LobbyCreateScreen from "$lib/screens/lobby-create-screen.svelte";
+	import ProfileScreen from "$lib/screens/profile-screen.svelte";
 	import GameShell from "$lib/game/game-shell.svelte";
 	import { pushState } from "$app/navigation";
 	import { page } from "$app/state";
@@ -67,6 +68,8 @@
 				pushState("", { screen: "game", gameId: appScreen.gameId });
 			} else if (appScreen.screen === "lobby-create") {
 				pushState("", { screen: "lobby-create" });
+			} else if (appScreen.screen === "profile") {
+				pushState("", { screen: "profile" });
 			}
 		}
 	});
@@ -83,6 +86,8 @@
 {#if session.status === "authenticated"}
 	{#if appScreen.screen === "lobby-create"}
 		<LobbyCreateScreen />
+	{:else if appScreen.screen === "profile"}
+		<ProfileScreen />
 	{:else if appScreen.screen === "game" && appScreen.gameId !== null}
 		<GameShell />
 	{:else}