feat(gateway): wire the wallet.order edge call for the direct rail

Add the WalletOrderRequest / WalletOrderResponse FlatBuffers messages and the
wallet.order Connect op: the gateway decodes the order request, forwards it to
the backend POST /wallet/order and returns the created order id plus the
provider launch URL the client opens. Regenerate the committed Go and TS
FlatBuffers code.

pkg/fbs/scrabblefb/WalletOrderRequest.go

@@ -0,0 +1,60 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package scrabblefb
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type WalletOrderRequest struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsWalletOrderRequest(buf []byte, offset flatbuffers.UOffsetT) *WalletOrderRequest {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &WalletOrderRequest{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func FinishWalletOrderRequestBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.Finish(offset)
+}
+
+func GetSizePrefixedRootAsWalletOrderRequest(buf []byte, offset flatbuffers.UOffsetT) *WalletOrderRequest {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &WalletOrderRequest{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func FinishSizePrefixedWalletOrderRequestBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.FinishSizePrefixed(offset)
+}
+
+func (rcv *WalletOrderRequest) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *WalletOrderRequest) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *WalletOrderRequest) ProductId() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func WalletOrderRequestStart(builder *flatbuffers.Builder) {
+	builder.StartObject(1)
+}
+func WalletOrderRequestAddProductId(builder *flatbuffers.Builder, productId flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(productId), 0)
+}
+func WalletOrderRequestEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}