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/tests/e2e/lobby-flow.spec.ts

@@ -251,7 +251,7 @@ async function completeLogin(page: Page): Promise<void> {
 	await page.getByTestId("login-code-input").fill("123456");
 	await page.getByTestId("login-code-submit").click();
 	// Sign-in switches the in-memory screen to the lobby.
-	await expect(page.getByTestId("device-session-id")).toBeVisible();
+	await expect(page.getByTestId("lobby-account-name")).toBeVisible();
 }
 
 test.describe("Phase 8 — lobby flow", () => {