style(mui): DataTable bold-cell option; restore SPZ/Aktualni-km emphasis + mono Menlo fallback

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/pages/Vehicles.tsx

@@ -230,7 +230,7 @@ export default function Vehicles() {
   }
 
   const columns: DataColumn<Vehicle>[] = [
-    { key: "spz", header: "SPZ", mono: true, render: (v) => v.spz },
+    { key: "spz", header: "SPZ", mono: true, bold: true, render: (v) => v.spz },
     { key: "name", header: "Název", render: (v) => v.name },
     {
       key: "brand",
@@ -250,6 +250,7 @@ export default function Vehicles() {
       header: "Aktuální km",
       align: "right",
       mono: true,
+      bold: true,
       render: (v) => `${formatKm(v.current_km)} km`,
     },
     {