Fix Laravel 5.5 compatibility issues - view helpers, collections, and auth routes

- Replace {{ url() }} with {{ url('/') }} in all blade templates to fix object-to-string conversion errors
- Update TeamStoreModel::selectTeamStoreGroupByCartKey() to use first() instead of get() for Laravel 5.5 Collections
- Fix TeamStoreController to access object properties directly instead of using array syntax [0]
- Update authentication routes to use Laravel 5.5 method names (showLoginForm, login, logout)
- Update login/register links from /auth/login to /login throughout views (navbar, app, auth pages)
- Verify cart, login, and register pages working with HTTP 200 status

resources/views/app.blade.php

@@ -57,8 +57,8 @@
 
 				<ul class="nav navbar-nav navbar-right">
 					@if (Auth::guest())
-						<li><a href="{{ url('/auth/login') }}">Login</a></li>
-						<li><a href="{{ url('/auth/register') }}">Register</a></li>
+					<li><a href="{{ url('/login') }}">Login</a></li>
+					<li><a href="{{ url('/register') }}">Register</a></li>
 					@else
 						<li class="dropdown">
 							<a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-expanded="false">{{ Auth::user()->username }} <span class="caret"></span></a>