phase 8: lobby UI + cross-stack lobby command catalog + TS FlatBuffers

- Extend pkg/model/lobby and pkg/schema/fbs/lobby.fbs with public-games
  list, my-applications/invites lists, game-create, application-submit,
  invite-redeem/decline. Mirror the matching transcoder pairs and Go
  fixture round-trip tests.
- Wire the seven new lobby message types through
  gateway/internal/backendclient/{routes,lobby_commands}.go with
  per-command REST helpers, JSON-tolerant decoding of backend wire
  shapes, and httptest-based unit coverage for success / 4xx / 5xx /
  503 across each command.
- Introduce TS-side FlatBuffers via the `flatbuffers` runtime dep, a
  `make fbs-ts` target driving flatc, and the generated bindings under
  ui/frontend/src/proto/galaxy/fbs. Phase 7's `user.account.get` decode
  now uses these bindings as well, closing the JSON.parse vs
  FlatBuffers gap that would have failed against a real local stack.
- Replace the placeholder lobby with five sections (my games, pending
  invitations, my applications, public games, create new game) and the
  /lobby/create form. Submit-application uses an inline race-name
  form on the public-game card; create-game keeps name / description /
  turn_schedule / enrollment_ends_at always visible and the rest under
  an Advanced toggle with TS-side defaults.
- Update lobby/+page.svelte to throw LobbyError on non-ok result codes;
  GalaxyClient.executeCommand now returns { resultCode, payloadBytes }.
- Vitest binding round-trips, lobby.ts wrapper unit tests, lobby-page
  + lobby-create component tests, Playwright lobby-flow.spec covering
  create / submit / accept across all four projects. Phase 7 e2e was
  migrated to the FlatBuffers fixtures and to click+fill against the
  Safari-autofill readonly inputs.
- Mark Phase 8 done in ui/PLAN.md, mirror the wire-format note into
  Phase 7, append the new lobby commands to gateway/README.md and
  docs/ARCHITECTURE.md, add ui/docs/lobby.md.

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

ui/frontend/src/api/galaxy-client.ts

@@ -46,6 +46,11 @@ export interface GalaxyClientOptions {
 
 const PROTOCOL_VERSION = "v1";
 
+export interface ExecuteCommandResult {
+	resultCode: string;
+	payloadBytes: Uint8Array;
+}
+
 export class GalaxyClient {
 	private readonly core: Core;
 	private readonly edge: EdgeGatewayClient;
@@ -72,7 +77,7 @@ export class GalaxyClient {
 		messageType: string,
 		payload: Uint8Array,
 		traceId = "",
-	): Promise<Uint8Array> {
+	): Promise<ExecuteCommandResult> {
 		const requestId = this.requestIdFactory();
 		const timestampMs = this.clock();
 		const payloadHash = await this.sha256(payload);
@@ -103,7 +108,10 @@ export class GalaxyClient {
 		);
 
 		this.verifyResponse(response, requestId);
-		return response.payloadBytes;
+		return {
+			resultCode: response.resultCode,
+			payloadBytes: response.payloadBytes,
+		};
 	}
 
 	private verifyResponse(