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>

pkg/schema/fbs/lobby/ApplicationSummary.go

@@ -0,0 +1,134 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package lobby
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type ApplicationSummary struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsApplicationSummary(buf []byte, offset flatbuffers.UOffsetT) *ApplicationSummary {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &ApplicationSummary{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func FinishApplicationSummaryBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.Finish(offset)
+}
+
+func GetSizePrefixedRootAsApplicationSummary(buf []byte, offset flatbuffers.UOffsetT) *ApplicationSummary {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &ApplicationSummary{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func FinishSizePrefixedApplicationSummaryBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.FinishSizePrefixed(offset)
+}
+
+func (rcv *ApplicationSummary) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *ApplicationSummary) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *ApplicationSummary) ApplicationId() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *ApplicationSummary) GameId() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *ApplicationSummary) ApplicantUserId() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *ApplicationSummary) RaceName() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(10))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *ApplicationSummary) Status() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(12))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *ApplicationSummary) CreatedAtMs() int64 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(14))
+	if o != 0 {
+		return rcv._tab.GetInt64(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *ApplicationSummary) MutateCreatedAtMs(n int64) bool {
+	return rcv._tab.MutateInt64Slot(14, n)
+}
+
+func (rcv *ApplicationSummary) DecidedAtMs() int64 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(16))
+	if o != 0 {
+		return rcv._tab.GetInt64(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *ApplicationSummary) MutateDecidedAtMs(n int64) bool {
+	return rcv._tab.MutateInt64Slot(16, n)
+}
+
+func ApplicationSummaryStart(builder *flatbuffers.Builder) {
+	builder.StartObject(7)
+}
+func ApplicationSummaryAddApplicationId(builder *flatbuffers.Builder, applicationId flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(applicationId), 0)
+}
+func ApplicationSummaryAddGameId(builder *flatbuffers.Builder, gameId flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(gameId), 0)
+}
+func ApplicationSummaryAddApplicantUserId(builder *flatbuffers.Builder, applicantUserId flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(2, flatbuffers.UOffsetT(applicantUserId), 0)
+}
+func ApplicationSummaryAddRaceName(builder *flatbuffers.Builder, raceName flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(3, flatbuffers.UOffsetT(raceName), 0)
+}
+func ApplicationSummaryAddStatus(builder *flatbuffers.Builder, status flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(4, flatbuffers.UOffsetT(status), 0)
+}
+func ApplicationSummaryAddCreatedAtMs(builder *flatbuffers.Builder, createdAtMs int64) {
+	builder.PrependInt64Slot(5, createdAtMs, 0)
+}
+func ApplicationSummaryAddDecidedAtMs(builder *flatbuffers.Builder, decidedAtMs int64) {
+	builder.PrependInt64Slot(6, decidedAtMs, 0)
+}
+func ApplicationSummaryEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}