Add Shopify inventory sync and order webhook

- Migration: shopify_variant_id on products_sizes, shopify_order_id on products_sales
- ShopifyService: paginated REST client (2024-10 API)
- shopify:map — one-time command to link variants by SKU
- shopify:sync — reconciliation command (Shopify is master)
- VerifyShopifyWebhook middleware: HMAC-SHA256 verification
- ShopifyWebhookController: idempotent orders/paid handler, FIFO inventory deduction
- Webhook route: POST /api/webhooks/shopify/orders-paid

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

app/Http/Controllers/ShopifyWebhookController.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace App\Http\Controllers;
+
+use App\Models\ProductInventory;
+use App\Models\ProductSale;
+use App\Models\ProductSize;
+use Illuminate\Http\Request;
+use Illuminate\Http\Response;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Log;
+
+class ShopifyWebhookController extends Controller
+{
+    public function ordersPaid(Request $request): Response
+    {
+        $order   = $request->json()->all();
+        $orderId = (string) ($order['id'] ?? '');
+
+        // Idempotency: ignore already-processed orders
+        if (ProductSale::where('shopify_order_id', $orderId)->exists()) {
+            return response('', 200);
+        }
+
+        DB::transaction(function () use ($order, $orderId) {
+            foreach ($order['line_items'] ?? [] as $item) {
+                $variantId = (string) ($item['variant_id'] ?? '');
+                $quantity  = (int)   ($item['quantity']   ?? 0);
+
+                if (!$variantId || $quantity <= 0) {
+                    continue;
+                }
+
+                $size = ProductSize::where('shopify_variant_id', $variantId)->first();
+
+                if (!$size) {
+                    Log::warning('Shopify webhook: unbekannte Variant-ID', [
+                        'variant_id' => $variantId,
+                        'order_id'   => $orderId,
+                    ]);
+                    continue;
+                }
+
+                // FIFO: älteste verfügbare Einheiten ausbuchen
+                ProductInventory::where('size_id', $size->id)
+                    ->whereNull('out_at')
+                    ->oldest()
+                    ->limit($quantity)
+                    ->update(['out_at' => now()]);
+
+                ProductSale::create([
+                    'product_id'       => $size->product_id,
+                    'size_id'          => $size->id,
+                    'amount'           => $quantity,
+                    'sold_at'          => now(),
+                    'shopify_order_id' => $orderId,
+                ]);
+            }
+        });
+
+        return response('', 200);
+    }
+}

app/Http/Middleware/VerifyShopifyWebhook.php

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+<?php
+
+namespace App\Http\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+use Symfony\Component\HttpFoundation\Response;
+
+class VerifyShopifyWebhook
+{
+    public function handle(Request $request, Closure $next): Response
+    {
+        $hmac   = $request->header('X-Shopify-Hmac-Sha256');
+        $secret = config('services.shopify.webhook_secret');
+
+        if (!$hmac || !$secret) {
+            abort(401);
+        }
+
+        $computed = base64_encode(hash_hmac('sha256', $request->getContent(), $secret, true));
+
+        if (!hash_equals($computed, $hmac)) {
+            abort(401);
+        }
+
+        return $next($request);
+    }
+}