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/InviteSummary.go

@@ -0,0 +1,171 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package lobby
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type InviteSummary struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsInviteSummary(buf []byte, offset flatbuffers.UOffsetT) *InviteSummary {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &InviteSummary{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func FinishInviteSummaryBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.Finish(offset)
+}
+
+func GetSizePrefixedRootAsInviteSummary(buf []byte, offset flatbuffers.UOffsetT) *InviteSummary {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &InviteSummary{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func FinishSizePrefixedInviteSummaryBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.FinishSizePrefixed(offset)
+}
+
+func (rcv *InviteSummary) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *InviteSummary) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *InviteSummary) InviteId() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *InviteSummary) GameId() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *InviteSummary) InviterUserId() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *InviteSummary) InvitedUserId() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(10))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *InviteSummary) Code() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(12))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *InviteSummary) RaceName() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(14))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *InviteSummary) Status() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(16))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *InviteSummary) CreatedAtMs() int64 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(18))
+	if o != 0 {
+		return rcv._tab.GetInt64(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *InviteSummary) MutateCreatedAtMs(n int64) bool {
+	return rcv._tab.MutateInt64Slot(18, n)
+}
+
+func (rcv *InviteSummary) ExpiresAtMs() int64 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(20))
+	if o != 0 {
+		return rcv._tab.GetInt64(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *InviteSummary) MutateExpiresAtMs(n int64) bool {
+	return rcv._tab.MutateInt64Slot(20, n)
+}
+
+func (rcv *InviteSummary) DecidedAtMs() int64 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(22))
+	if o != 0 {
+		return rcv._tab.GetInt64(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *InviteSummary) MutateDecidedAtMs(n int64) bool {
+	return rcv._tab.MutateInt64Slot(22, n)
+}
+
+func InviteSummaryStart(builder *flatbuffers.Builder) {
+	builder.StartObject(10)
+}
+func InviteSummaryAddInviteId(builder *flatbuffers.Builder, inviteId flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(inviteId), 0)
+}
+func InviteSummaryAddGameId(builder *flatbuffers.Builder, gameId flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(gameId), 0)
+}
+func InviteSummaryAddInviterUserId(builder *flatbuffers.Builder, inviterUserId flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(2, flatbuffers.UOffsetT(inviterUserId), 0)
+}
+func InviteSummaryAddInvitedUserId(builder *flatbuffers.Builder, invitedUserId flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(3, flatbuffers.UOffsetT(invitedUserId), 0)
+}
+func InviteSummaryAddCode(builder *flatbuffers.Builder, code flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(4, flatbuffers.UOffsetT(code), 0)
+}
+func InviteSummaryAddRaceName(builder *flatbuffers.Builder, raceName flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(5, flatbuffers.UOffsetT(raceName), 0)
+}
+func InviteSummaryAddStatus(builder *flatbuffers.Builder, status flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(6, flatbuffers.UOffsetT(status), 0)
+}
+func InviteSummaryAddCreatedAtMs(builder *flatbuffers.Builder, createdAtMs int64) {
+	builder.PrependInt64Slot(7, createdAtMs, 0)
+}
+func InviteSummaryAddExpiresAtMs(builder *flatbuffers.Builder, expiresAtMs int64) {
+	builder.PrependInt64Slot(8, expiresAtMs, 0)
+}
+func InviteSummaryAddDecidedAtMs(builder *flatbuffers.Builder, decidedAtMs int64) {
+	builder.PrependInt64Slot(9, decidedAtMs, 0)
+}
+func InviteSummaryEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}