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/scrabble.fbs

@@ -873,6 +873,18 @@ table WalletBuyRequest {
   product_id:string;
 }
 
+// WalletOrderRequest opens a money order to fund a chip pack: the pack to buy.
+table WalletOrderRequest {
+  product_id:string;
+}
+
+// WalletOrderResponse returns the created order id and the provider launch URL the client opens
+// (the Robokassa hosted-payment page); chips are credited later, by the verified server callback.
+table WalletOrderResponse {
+  order_id:string;
+  redirect_url:string;
+}
+
 // CatalogAtom is one atom line of a storefront product: the base value type it grants
 // ("chips"/"hints"/"noads_days"/"tournament") and how many of it the product carries.
 table CatalogAtom {