Shorten default barcode height -- printer default (~162 dots) prints noticeably tall

lib/receipt_builder.rb

@@ -87,8 +87,10 @@ class ReceiptBuilder
     self
   end
 
-  # Native ESC/POS EAN-13
-  def ean13(code)
+  # Native ESC/POS EAN-13. height is in dots (GS h) -- the printer's default
+  # (~162 dots) prints noticeably tall; 50 is a shorter, still-scannable size.
+  def ean13(code, height: 50)
+    @buffer << "\x1D\x68" << height.chr # GS h n -- set barcode height
     @buffer << "\x1D\x6B\x02" << code.b << "\x00"
     self
   end