Fix admin route access and backend configuration

- Added /admin redirect to login page in nginx config
- Fixed backend server.js route ordering for proper admin handling
- Updated authentication middleware and routes
- Added user management routes
- Configured PostgreSQL integration
- Updated environment configuration

Sky_Art_shop/Views/Shared/Components/Navigation/Default.cshtml

@@ -0,0 +1,16 @@
+@model List<SkyArtShop.Models.MenuItem>
+
+<ul class="nav-menu">
+    @foreach (var item in Model)
+    {
+        var currentController = ViewContext.RouteData.Values["Controller"]?.ToString();
+        var isActive = item.Url.TrimStart('/').Equals(currentController, StringComparison.OrdinalIgnoreCase) ||
+        (item.Url == "/" && currentController == "Home");
+
+        <li>
+            <a href="@item.Url" class="@(isActive ? "active" : "")" @(item.OpenInNewTab ? "target='_blank'" : "")>
+                @item.Label
+            </a>
+        </li>
+    }
+</ul>