feat(pay): switch checkout counter to SPA redirect + JSON API

- redirect `/pay/checkout-counter/:trade_id` to `/cashier/:trade_id`
- add `/pay/checkout-counter-resp/:trade_id` for checkout JSON payload
- remove embedded `static` release and keep `www` as the web bundle source
- regenerate PWA/www assets and move chain icons to `/www/images/chains`

src/route/router.go

@@ -27,7 +27,15 @@ func RegisterRoute(e *echo.Echo) {
 	})
 
 	payRoute := e.Group("/pay")
-	payRoute.GET("/checkout-counter/:trade_id", comm.Ctrl.CheckoutCounter)
+	payRoute.GET("/checkout-counter/:trade_id", func(ctx echo.Context) error {
+		tradeId := ctx.Param("trade_id")
+
+		targetURL := fmt.Sprintf("/cashier/%s", tradeId)
+
+		return ctx.Redirect(http.StatusMovedPermanently, targetURL)
+	})
+
+	payRoute.GET("/checkout-counter-resp/:trade_id", comm.Ctrl.CheckoutCounter)
 	payRoute.GET("/check-status/:trade_id", comm.Ctrl.CheckStatus)
 	payRoute.POST("/switch-network", comm.Ctrl.SwitchNetwork)