Fix 2-page label: reset @page margin to 0, shrink barcode to fit

The custom @page margins conflicted with browser minimum margins,
causing overflow. Now @page margin is 0, barcode height 8mm→6mm,
scale 3→2, text size 12→10 so content fits within 29mm even with
browser minimum margins selected.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/server/barcode.ts

@@ -5,10 +5,10 @@ export async function generateBarcodeSvg(text: string): Promise<string> {
 	const buf = await bwipjs.toBuffer({
 		bcid: 'code128',
 		text,
-		scale: 3,
+		scale: 2,
 		height: 8,
 		includetext: true,
-		textsize: 12,
+		textsize: 10,
 		textxalign: 'center'
 	});