fix(ux): replace confirm() with ConfirmModal, fix dark-mode colors, add currency format

- Add reusable ConfirmModal component (themed, Escape key, focus trap)
- Replace all native confirm() calls in Orders, ProductLibrary, Materials, Admin, Billing
- Fix ValidationDialog (Upload.tsx) hardcoded bg-white/text-gray-* → semantic tokens
- Fix NewInvoiceModal (Billing.tsx) hardcoded colors → semantic tokens
- Add formatCurrency (Intl.NumberFormat de-DE/EUR) to NewProductOrder wizard
- Resolves audit issues C1, C3, M3

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/Orders.tsx

@@ -11,6 +11,7 @@ import { toast } from 'sonner'
 import { listOrders, searchOrders, deleteOrder } from '../api/orders'
 import { fetchThumbnailBlob } from '../api/cad'
 import type { Order, OrderDetail, OrderItem } from '../api/orders'
+import ConfirmModal from '../components/ConfirmModal'
 // ── Constants ────────────────────────────────────────────────────────────────
 
 const STATUSES = ['draft', 'submitted', 'processing', 'completed', 'rejected'] as const
@@ -49,6 +50,7 @@ export default function OrdersPage() {
   const [dateTo, setDateTo] = useState('')
   const [showFilters, setShowFilters] = useState(false)
   const [selected, setSelected] = useState<Set<string>>(new Set())
+  const [confirmState, setConfirmState] = useState<{ open: boolean; title: string; message: string; onConfirm: () => void }>({ open: false, title: '', message: '', onConfirm: () => {} })
 
   // Debounce the search input (400 ms)
   useEffect(() => {
@@ -161,8 +163,15 @@ export default function OrdersPage() {
   const handleDeleteSelected = () => {
     const ids = [...selected]
     if (!ids.length) return
-    if (!confirm(`Delete ${ids.length} order${ids.length > 1 ? 's' : ''}? This cannot be undone.`)) return
-    deleteMut.mutate(ids)
+    setConfirmState({
+      open: true,
+      title: `Delete ${ids.length} order${ids.length > 1 ? 's' : ''}`,
+      message: 'This cannot be undone.',
+      onConfirm: () => {
+        deleteMut.mutate(ids)
+        setConfirmState((s) => ({ ...s, open: false }))
+      },
+    })
   }
 
   // ── Render ───────────────────────────────────────────────────────────────
@@ -351,6 +360,14 @@ export default function OrdersPage() {
         />
       )}
 
+      <ConfirmModal
+        open={confirmState.open}
+        title={confirmState.title}
+        message={confirmState.message}
+        onConfirm={confirmState.onConfirm}
+        onCancel={() => setConfirmState((s) => ({ ...s, open: false }))}
+      />
+
       {/* ── Bulk delete bar ───────────────────────────────────────────────── */}
       {selected.size > 0 && (
         <div className="fixed bottom-6 left-1/2 -translate-x-1/2 ml-[120px] z-50