feat(orders): PDF footer = issuer name+email, 'Zobrazit objednávku' button, per-currency list totals

- Issued-order PDF: drop the Vystavil/Schválil signature row; footer now shows
  'Vystavil: <name>' + 'E-mail: <email>' from the logged-in user (authData).
- IssuedOrderDetail PDF button 'Export PDF' -> 'Zobrazit objednávku' (already
  opens inline like invoices' 'Zobrazit fakturu').
- New /orders/stats + /issued-orders/stats endpoints sum order total (incl VAT)
  per currency across the active filter; rendered as 'Celkem: …' beneath both
  the received and issued lists. formatMultiCurrency lifted to a shared util.

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

src/admin/pages/IssuedOrderDetail.tsx

@@ -956,7 +956,7 @@ export default function IssuedOrderDetail() {
                 )
               }
             >
-              Export PDF
+              Zobrazit objednávku
             </Button>
           )}
           {/* ── Create mode: two-button save ── */}