Refactor navigation structure and API routes

- Centralize user menu, sidebar items, and breadcrumb logic.
- Map consistent API endpoints in `customerRoutes`.
- Replace inline route definitions with reusable constants.
- Refactor auth configuration file location.
- Improve `<Link>` usage to replace static `<a>` elements.
- Adjust sidebar and dropdown components to use dynamic navigation configurations.

internal_frontend/app/api/auth/[...nextauth]/route.ts

@@ -1,5 +1,5 @@
 import NextAuth from "next-auth";
-import {authOptions} from "@/lib/auth/authOptions";
+import {authOptions} from "@/lib/api/auth/authOptions";
 
 const handler = NextAuth(authOptions);
 export {handler as GET, handler as POST};

internal_frontend/app/api/customers/[id]/route.ts

@@ -1,9 +1,10 @@
 import {NextRequest, NextResponse} from "next/server";
 import {serverCall} from "@/lib/api/serverCall";
+import {customerRoutes} from "@/app/api/customers/customerRoutes";
 
 export async function GET(request: NextRequest) {
     const id = request.url.split('/').pop();
-    const response = await serverCall(`/customers/${id}`, "GET");
+    const response = await serverCall(customerRoutes.getById(id!), "GET");
 
     if (!response.ok) {
         return NextResponse.json({error: "Customer not found"}, {status: 404});

internal_frontend/app/api/customers/customerRoutes.ts

@@ -1,4 +1,5 @@
 export const customerRoutes = {
     create: "/customers",
     validate: "/customers/validate",
+    getById: (id: string) => `/customers/${id}`,
 };

internal_frontend/app/api/customers/route.ts

@@ -1,14 +1,15 @@
 import {NextRequest, NextResponse} from "next/server";
 import {serverCall} from "@/lib/api/serverCall";
+import {customerRoutes} from "@/app/api/customers/customerRoutes";
 
 export async function GET() {
-    const data = await serverCall("/customers", "GET");
+    const data = await serverCall(customerRoutes.create, "GET");
     const customers = await data.json();
     return NextResponse.json(customers);
 }
 
 export async function POST(req: NextRequest) {
     const body = await req.json()
-    const result = await serverCall("/customers", "POST", body);
+    const result = await serverCall(customerRoutes.create, "POST", body);
     return NextResponse.json(result.json());
 }