Remove CustomerRepository and replace with direct API calls

- Remove `CustomerRepository` and its methods for customer management and caching.
- Refactor customer-related pages (`[id]/page.tsx`, `customers/page.tsx`) to use direct `fetch` API calls.
- Update breadcrumb resolver to fetch data directly from the API.
- Simplify `addCustomer` use case to avoid repository dependency.

internal_frontend/app/customers/[id]/page.tsx

@@ -11,7 +11,6 @@ import CustomerInformationContent from "@/components/customers/details/sub/Conta
 import CustomerPhoneNumberContent from "@/components/customers/details/sub/CustomerPhoneNumberContent";
 import CustomerNotesContent from "@/components/customers/details/sub/CustomerNotesContent";
 import {Customer} from "@/services/customers/entities/customer";
-import {CustomerRepository} from "@/services/customers/repositories/customerRepository";
 
 export default function CustomerDetailPage() {
     const router = useRouter();
@@ -33,16 +32,22 @@ export default function CustomerDetailPage() {
         setLoading(true);
         setError(null);
 
-        CustomerRepository.getById(id)
-            .then((result) => {
+        fetch(`/api/customers/${id}`)
+            .then(async (response) => {
                 if (!isMounted) return;
 
-                if (!result) {
+                if (response.status === 404) {
                     setError("Kunde nicht gefunden");
                     setCustomer(null);
-                } else {
-                    setCustomer(result);
+                    return;
                 }
+
+                if (!response.ok) {
+                    throw new Error(`Failed to fetch customer: ${response.statusText}`);
+                }
+
+                const result = await response.json();
+                setCustomer(result);
             })
             .catch((error) => {
                 if (!isMounted) return;
@@ -164,4 +169,4 @@ export default function CustomerDetailPage() {
             </Dialog>
         </div>
     );
-}
+}