Add PayPal, Stripe, CSV-Export; fix .env.production issue

- PayPal: Checkout-Integration via srmklive/paypal, Weiterleitung zu PayPal,
  Bestellung wird nach Capture automatisch auf payment_received gesetzt
- Stripe: Payment Elements im Checkout, Intent-API, Zahlung direkt bestätigt
- CSV-Export: Admin → Bestellungen → CSV exportieren (UTF-8 BOM für Excel)
- PayPal/Stripe nur sichtbar wenn Keys in .env gesetzt
- .env.example um PAYPAL_* und STRIPE_* Keys erweitert

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

app/Http/Controllers/Admin/OrderController.php

@@ -76,4 +76,39 @@ class OrderController extends Controller
     {
         return $this->invoiceService->generate($order)->download($this->invoiceService->filename($order));
     }
+
+    public function exportCsv()
+    {
+        $orders = Order::with(['items','billingAddress'])->orderByDesc('created_at')->get();
+
+        $rows = [];
+        $rows[] = ['Bestellnr.','Datum','Status','Zahlungsart','Kunde','E-Mail','Zwischensumme','Rabatt','Versand','Gesamt','MwSt.'];
+
+        foreach ($orders as $order) {
+            $addr = $order->billingAddress();
+            $rows[] = [
+                $order->order_number,
+                $order->created_at->format('d.m.Y H:i'),
+                Order::$statusLabels[$order->status] ?? $order->status,
+                Order::$paymentLabels[$order->payment_method] ?? $order->payment_method,
+                $addr ? $addr->full_name : ($order->guest_email ?? ''),
+                $order->guest_email ?? $order->user?->email ?? '',
+                number_format($order->subtotal, 2, ',', '.'),
+                number_format($order->discount_amount ?? 0, 2, ',', '.'),
+                number_format($order->shipping_cost, 2, ',', '.'),
+                number_format($order->total, 2, ',', '.'),
+                number_format($order->tax_total, 2, ',', '.'),
+            ];
+        }
+
+        $csv = "\xEF\xBB\xBF"; // UTF-8 BOM für Excel
+        foreach ($rows as $row) {
+            $csv .= implode(';', array_map(fn($v) => '"' . str_replace('"', '""', $v) . '"', $row)) . "\n";
+        }
+
+        return response($csv, 200, [
+            'Content-Type'        => 'text/csv; charset=UTF-8',
+            'Content-Disposition' => 'attachment; filename="bestellungen-' . date('Y-m-d') . '.csv"',
+        ]);
+    }
 }