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/proto/galaxy/fbs/user/active-sanction.ts

@@ -0,0 +1,147 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+/* eslint-disable @typescript-eslint/no-unused-vars, @typescript-eslint/no-explicit-any, @typescript-eslint/no-non-null-assertion */
+
+import * as flatbuffers from 'flatbuffers';
+
+import { ActorRef, ActorRefT } from './actor-ref.js';
+
+
+export class ActiveSanction implements flatbuffers.IUnpackableObject<ActiveSanctionT> {
+  bb: flatbuffers.ByteBuffer|null = null;
+  bb_pos = 0;
+  __init(i:number, bb:flatbuffers.ByteBuffer):ActiveSanction {
+  this.bb_pos = i;
+  this.bb = bb;
+  return this;
+}
+
+static getRootAsActiveSanction(bb:flatbuffers.ByteBuffer, obj?:ActiveSanction):ActiveSanction {
+  return (obj || new ActiveSanction()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+static getSizePrefixedRootAsActiveSanction(bb:flatbuffers.ByteBuffer, obj?:ActiveSanction):ActiveSanction {
+  bb.setPosition(bb.position() + flatbuffers.SIZE_PREFIX_LENGTH);
+  return (obj || new ActiveSanction()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+sanctionCode():string|null
+sanctionCode(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+sanctionCode(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 4);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+scope():string|null
+scope(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+scope(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 6);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+reasonCode():string|null
+reasonCode(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+reasonCode(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 8);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+actor(obj?:ActorRef):ActorRef|null {
+  const offset = this.bb!.__offset(this.bb_pos, 10);
+  return offset ? (obj || new ActorRef()).__init(this.bb!.__indirect(this.bb_pos + offset), this.bb!) : null;
+}
+
+appliedAtMs():bigint {
+  const offset = this.bb!.__offset(this.bb_pos, 12);
+  return offset ? this.bb!.readInt64(this.bb_pos + offset) : BigInt('0');
+}
+
+expiresAtMs():bigint {
+  const offset = this.bb!.__offset(this.bb_pos, 14);
+  return offset ? this.bb!.readInt64(this.bb_pos + offset) : BigInt('0');
+}
+
+static startActiveSanction(builder:flatbuffers.Builder) {
+  builder.startObject(6);
+}
+
+static addSanctionCode(builder:flatbuffers.Builder, sanctionCodeOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(0, sanctionCodeOffset, 0);
+}
+
+static addScope(builder:flatbuffers.Builder, scopeOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(1, scopeOffset, 0);
+}
+
+static addReasonCode(builder:flatbuffers.Builder, reasonCodeOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(2, reasonCodeOffset, 0);
+}
+
+static addActor(builder:flatbuffers.Builder, actorOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(3, actorOffset, 0);
+}
+
+static addAppliedAtMs(builder:flatbuffers.Builder, appliedAtMs:bigint) {
+  builder.addFieldInt64(4, appliedAtMs, BigInt('0'));
+}
+
+static addExpiresAtMs(builder:flatbuffers.Builder, expiresAtMs:bigint) {
+  builder.addFieldInt64(5, expiresAtMs, BigInt('0'));
+}
+
+static endActiveSanction(builder:flatbuffers.Builder):flatbuffers.Offset {
+  const offset = builder.endObject();
+  return offset;
+}
+
+
+unpack(): ActiveSanctionT {
+  return new ActiveSanctionT(
+    this.sanctionCode(),
+    this.scope(),
+    this.reasonCode(),
+    (this.actor() !== null ? this.actor()!.unpack() : null),
+    this.appliedAtMs(),
+    this.expiresAtMs()
+  );
+}
+
+
+unpackTo(_o: ActiveSanctionT): void {
+  _o.sanctionCode = this.sanctionCode();
+  _o.scope = this.scope();
+  _o.reasonCode = this.reasonCode();
+  _o.actor = (this.actor() !== null ? this.actor()!.unpack() : null);
+  _o.appliedAtMs = this.appliedAtMs();
+  _o.expiresAtMs = this.expiresAtMs();
+}
+}
+
+export class ActiveSanctionT implements flatbuffers.IGeneratedObject {
+constructor(
+  public sanctionCode: string|Uint8Array|null = null,
+  public scope: string|Uint8Array|null = null,
+  public reasonCode: string|Uint8Array|null = null,
+  public actor: ActorRefT|null = null,
+  public appliedAtMs: bigint = BigInt('0'),
+  public expiresAtMs: bigint = BigInt('0')
+){}
+
+
+pack(builder:flatbuffers.Builder): flatbuffers.Offset {
+  const sanctionCode = (this.sanctionCode !== null ? builder.createString(this.sanctionCode!) : 0);
+  const scope = (this.scope !== null ? builder.createString(this.scope!) : 0);
+  const reasonCode = (this.reasonCode !== null ? builder.createString(this.reasonCode!) : 0);
+  const actor = (this.actor !== null ? this.actor!.pack(builder) : 0);
+
+  ActiveSanction.startActiveSanction(builder);
+  ActiveSanction.addSanctionCode(builder, sanctionCode);
+  ActiveSanction.addScope(builder, scope);
+  ActiveSanction.addReasonCode(builder, reasonCode);
+  ActiveSanction.addActor(builder, actor);
+  ActiveSanction.addAppliedAtMs(builder, this.appliedAtMs);
+  ActiveSanction.addExpiresAtMs(builder, this.expiresAtMs);
+
+  return ActiveSanction.endActiveSanction(builder);
+}
+}