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/api/account.ts

@@ -0,0 +1,132 @@
+// Typed wrappers around `GalaxyClient.executeCommand` for the user-
+// account command catalog. Each wrapper builds a FlatBuffers request
+// payload via the generated TS bindings, calls `executeCommand`, then
+// decodes the `AccountResponse` reply. Errors with a non-`ok`
+// `result_code` surface as a thrown `AccountError` carrying the
+// canonical backend code (`invalid_request`, `subject_not_found`,
+// `forbidden`, `conflict`, `internal_error`).
+
+import { Builder, ByteBuffer } from "flatbuffers";
+
+import type { GalaxyClient } from "./galaxy-client";
+import {
+	AccountResponse,
+	AccountView,
+	ErrorResponse as FbsErrorResponse,
+	GetMyAccountRequest,
+	UpdateMyProfileRequest,
+	UpdateMySettingsRequest,
+} from "../proto/galaxy/fbs/user";
+
+const RESULT_CODE_OK = "ok";
+
+export class AccountError extends Error {
+	readonly code: string;
+	readonly resultCode: string;
+
+	constructor(resultCode: string, code: string, message: string) {
+		super(message);
+		this.name = "AccountError";
+		this.resultCode = resultCode;
+		this.code = code;
+	}
+}
+
+export interface Account {
+	userId: string;
+	email: string;
+	userName: string;
+	displayName: string;
+	preferredLanguage: string;
+	timeZone: string;
+	declaredCountry: string;
+}
+
+export async function getMyAccount(client: GalaxyClient): Promise<Account> {
+	const builder = new Builder(32);
+	GetMyAccountRequest.startGetMyAccountRequest(builder);
+	builder.finish(GetMyAccountRequest.endGetMyAccountRequest(builder));
+	const payload = await execute(client, "user.account.get", builder.asUint8Array());
+	return decodeAccountResponse(payload);
+}
+
+export async function updateMyProfile(
+	client: GalaxyClient,
+	displayName: string,
+): Promise<Account> {
+	const builder = new Builder(128);
+	const displayNameOff = builder.createString(displayName);
+	UpdateMyProfileRequest.startUpdateMyProfileRequest(builder);
+	UpdateMyProfileRequest.addDisplayName(builder, displayNameOff);
+	builder.finish(UpdateMyProfileRequest.endUpdateMyProfileRequest(builder));
+	const payload = await execute(client, "user.profile.update", builder.asUint8Array());
+	return decodeAccountResponse(payload);
+}
+
+export async function updateMySettings(
+	client: GalaxyClient,
+	preferredLanguage: string,
+	timeZone: string,
+): Promise<Account> {
+	const builder = new Builder(128);
+	const preferredLanguageOff = builder.createString(preferredLanguage);
+	const timeZoneOff = builder.createString(timeZone);
+	UpdateMySettingsRequest.startUpdateMySettingsRequest(builder);
+	UpdateMySettingsRequest.addPreferredLanguage(builder, preferredLanguageOff);
+	UpdateMySettingsRequest.addTimeZone(builder, timeZoneOff);
+	builder.finish(UpdateMySettingsRequest.endUpdateMySettingsRequest(builder));
+	const payload = await execute(client, "user.settings.update", builder.asUint8Array());
+	return decodeAccountResponse(payload);
+}
+
+async function execute(
+	client: GalaxyClient,
+	messageType: string,
+	payloadBytes: Uint8Array,
+): Promise<Uint8Array> {
+	const result = await client.executeCommand(messageType, payloadBytes);
+	if (result.resultCode !== RESULT_CODE_OK) {
+		throw decodeAccountError(result.resultCode, result.payloadBytes);
+	}
+	return result.payloadBytes;
+}
+
+function decodeAccountError(resultCode: string, payload: Uint8Array): AccountError {
+	let code = resultCode;
+	let message = resultCode;
+	try {
+		const errorResponse = FbsErrorResponse.getRootAsErrorResponse(new ByteBuffer(payload));
+		const body = errorResponse.error();
+		if (body) {
+			code = body.code() ?? resultCode;
+			message = body.message() ?? resultCode;
+		}
+	} catch (_err) {
+		// fall through with the raw result code
+	}
+	return new AccountError(resultCode, code, message);
+}
+
+function decodeAccountResponse(payload: Uint8Array): Account {
+	if (payload.length === 0) {
+		throw new AccountError("internal_error", "internal_error", "empty account response");
+	}
+	const response = AccountResponse.getRootAsAccountResponse(new ByteBuffer(payload));
+	const view = response.account();
+	if (view === null) {
+		throw new AccountError("internal_error", "internal_error", "account missing in response");
+	}
+	return decodeAccountView(view);
+}
+
+function decodeAccountView(view: AccountView): Account {
+	return {
+		userId: view.userId() ?? "",
+		email: view.email() ?? "",
+		userName: view.userName() ?? "",
+		displayName: view.displayName() ?? "",
+		preferredLanguage: view.preferredLanguage() ?? "",
+		timeZone: view.timeZone() ?? "",
+		declaredCountry: view.declaredCountry() ?? "",
+	};
+}