fix: PDF item names bold on Linux — font-weight 500→600

Linux lacks Segoe UI semibold, so weight 500 rendered as regular.
Changed to 600 which maps to bold on both Windows and Linux.

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

src/routes/admin/invoices-pdf.ts

@@ -699,7 +699,7 @@ export default async function invoicesPdfRoutes(
   }
   table.items tbody td.desc {
     font-size: 9.5pt;
-    font-weight: 500;
+    font-weight: 600;
     color: #1a1a1a;
   }
   table.items tbody td.total-cell { font-weight: 700; }

src/routes/admin/offers-pdf.ts

@@ -517,7 +517,7 @@ ${indentCSS}
   }
   table.items tbody td.desc {
     font-size: 10pt;
-    font-weight: 500;
+    font-weight: 600;
     color: #1a1a1a;
   }
   table.items tbody td.total-cell {