feat: rename invoice (RE-) to order confirmation (BE-) throughout the application

shop/components/invoice-pdf.tsx

@@ -117,10 +117,10 @@ export const InvoicePDF = ({ order, orderSnapshot, customer }: any) => {
           </View>
         </View>
 
-        <Text style={styles.title}>Bestellbestätigung / Rechnung</Text>
+        <Text style={styles.title}>Bestellbestätigung</Text>
 
         <View style={styles.section}>
-          <Text style={styles.label}>Rechnungsempfänger</Text>
+          <Text style={styles.label}>Besteller / Kunde</Text>
           <Text>{customer.company_name}</Text>
           <Text>{customer.first_name} {customer.last_name}</Text>
           <Text>{customer.address}</Text>