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/types/navigation/sidebar.ts

@@ -0,0 +1,12 @@
+import {LucideIcon} from "lucide-react";
+
+export interface MenuItem {
+    title: string;
+    url: string;
+    icon: LucideIcon;
+}
+
+export interface SubMenuItem {
+    title: string;
+    url: string;
+}