feat: Add product dependencies (requirements and exclusions) to database, admin UI and wizard validation

shop/components/order-wizard.tsx

@@ -139,6 +139,45 @@ export function OrderWizard({
       })
   }, [categories, selections, products, selectedBillingInterval])
 
+  // Product validation errors (requirements and exclusions)
+  const productValidationErrors = useMemo(() => {
+    const errors: string[] = []
+    const selectedProductIds = Object.values(selections)
+      .map(s => s.productId)
+      .filter((id): id is string => !!id)
+
+    selectedProductIds.forEach(prodId => {
+      const prod = products.find(p => p.id === prodId)
+      if (!prod) return
+
+      // Requirements check
+      if (prod.requirements && prod.requirements.length > 0) {
+        const missing = prod.requirements.filter(reqId => !selectedProductIds.includes(reqId))
+        if (missing.length > 0) {
+          const names = missing
+            .map(reqId => products.find(p => p.id === reqId)?.name || reqId)
+            .join(', ')
+          errors.push(`"${prod.name}" benötigt das Produkt: ${names}`)
+        }
+      }
+
+      // Exclusions check
+      if (prod.exclusions && prod.exclusions.length > 0) {
+        const conflicting = prod.exclusions.filter(exId => selectedProductIds.includes(exId))
+        if (conflicting.length > 0) {
+          const names = conflicting
+            .map(exId => products.find(p => p.id === exId)?.name || exId)
+            .join(', ')
+          errors.push(`"${prod.name}" schließt aus: ${names}`)
+        }
+      }
+    })
+
+    return errors
+  }, [selections, products])
+
+  const isNextStepDisabled = !allCategoriesFilled || productValidationErrors.length > 0
+
   // Total price calculations (split by billing interval)
   const { monthlyTotal, oneTimeTotal } = useMemo(() => {
     let monthly = 0
@@ -786,12 +825,18 @@ export function OrderWizard({
                         Bitte aus jeder Pflichtkategorie einen Artikel wählen.
                       </p>
                     )}
+                    {productValidationErrors.map((err, errIdx) => (
+                      <p key={errIdx} className="text-xs text-destructive flex items-center gap-1">
+                        <AlertCircle className="w-3 h-3 text-destructive" />
+                        {err}
+                      </p>
+                    ))}
                   </CardContent>
                   <CardFooter className="flex flex-col gap-2">
                     <Button
                       className="w-full h-12 text-lg"
                       onClick={nextStep}
-                      disabled={!allCategoriesFilled}
+                      disabled={isNextStepDisabled}
                     >
                       Weiter <ChevronRight className="ml-2 w-5 h-5" />
                     </Button>