feat: initialize project backend with Sanctum authentication and setup base CSS styles

backend/routes/api.php

@@ -0,0 +1,8 @@
+<?php
+
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Route;
+
+Route::get('/user', function (Request $request) {
+    return $request->user();
+})->middleware('auth:sanctum');