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/lib/navigation/breadcrumb-map.ts

@@ -1,5 +1,3 @@
-import {CustomerRepository} from "@/services/customers/repositories/customerRepository";
-
 export const breadcrumbMap: Record<string, string> = {
     'dashboard': 'Dashboard',
     'settings': 'Settings',
@@ -10,11 +8,21 @@ export const breadcrumbMap: Record<string, string> = {
 
 export const breadcrumbResolvers: Record<string, (id: string) => Promise<string>> = {
     "customers": async (id: string) => {
-        const customer = await CustomerRepository.getById(id);
-        if (!customer) return `ID: ${id}`;
+        try {
+            const response = await fetch(`/api/customers/${id}`);
+            if (!response.ok) {
+                return `ID: ${id}`;
+            }
 
-        if (customer.companyName) return `Firma: ${customer.companyName}`;
-        if (customer.name) return `Name: ${customer.name}`;
-        return `ID: ${id}`;
+            const customer = await response.json();
+            if (!customer) return `ID: ${id}`;
+
+            if (customer.companyName) return `Firma: ${customer.companyName}`;
+            if (customer.name) return `Name: ${customer.name}`;
+            return `ID: ${id}`;
+        } catch (error) {
+            console.error('Error fetching customer for breadcrumb:', error);
+            return `ID: ${id}`;
+        }
     },
-};
+};