fix(po): place stamp clear of the signature (no overlap)

Signatures/stamps aren't always transparent PNGs, so an opaque stamp would
cover the signature/name where it overlapped. Position the stamp to the right
of the centred signature with a 10px gap so it never overlays either.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

App/app/api/po/[id]/export/route.ts

@@ -478,11 +478,14 @@ export async function GET(request: NextRequest, { params }: Props) {
     const sigExt = signatureBase64 ? scaleToBox(signatureSize ?? { width: 360, height: 96 }, 165, 44) : null;
     const sigLeft = sigExt ? Math.round((SIG_BLOCK_PX - sigExt.width) / 2) : 0; // centred over the name
 
-    // Stamp / seal — drawn FIRST so it sits BEHIND the signature, tucked to its right.
+    // Stamp / seal — placed to the RIGHT of the signature with a gap, so it never
+    // overlays the signature or name (stamps/signatures aren't always transparent PNGs).
+    // Still drawn before the signature so it layers behind if they ever touch.
     if (stampImg) {
       const stampExt = scaleToBox(stampImg, 80, 66);
+      const STAMP_GAP = 10;
       const stampLeft = sigExt
-        ? Math.min(SIG_BLOCK_PX - stampExt.width, sigLeft + sigExt.width - Math.round(stampExt.width * 0.35))
+        ? Math.min(SIG_BLOCK_PX - stampExt.width, sigLeft + sigExt.width + STAMP_GAP)
         : SIG_BLOCK_PX - stampExt.width - 6;
       const stampId = wb.addImage({
         base64: stampImg.base64,