Show real exception details to admins on the error page (diagnostics)

Production hides the exception behind a generic 500, so a logged-in Admin couldn''t see why a page
(e.g. /Admin/Settings) failed. Surface the exception type/message/inner/stack on the /Error page ONLY
when the current user is in the Admin role; everyone else still sees the generic message.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/JobsMedical.Web/Pages/Error.cshtml

@@ -14,6 +14,15 @@
     </p>
 }
 
+@if (Model.AdminDetail is not null)
+{
+    <div style="margin:16px 0; padding:14px; border:1px solid var(--danger); border-radius:10px; background:#fff5f5; direction:ltr; text-align:left;">
+        <strong>🔧 جزئیات خطا (فقط برای ادمین)</strong>
+        @if (Model.AdminPath is not null) { <div style="margin:6px 0;"><code>@Model.AdminPath</code></div> }
+        <pre style="white-space:pre-wrap; word-break:break-word; font-size:12px; margin:8px 0 0; max-height:50vh; overflow:auto;">@Model.AdminDetail</pre>
+    </div>
+}
+
 <h3>Development Mode</h3>
 <p>
     Swapping to the <strong>Development</strong> environment displays detailed information about the error that occurred.

src/JobsMedical.Web/Pages/Error.cshtml.cs

@@ -1,4 +1,5 @@
 using System.Diagnostics;
+using Microsoft.AspNetCore.Diagnostics;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.AspNetCore.Mvc.RazorPages;
 
@@ -12,9 +13,24 @@ public class ErrorModel : PageModel
 
     public bool ShowRequestId => !string.IsNullOrEmpty(RequestId);
 
+    /// <summary>The real exception — shown ONLY to a logged-in Admin, so production 500s can be
+    /// diagnosed without server-log access. Hidden from everyone else.</summary>
+    public string? AdminDetail { get; private set; }
+    public string? AdminPath { get; private set; }
+
     public void OnGet()
     {
         RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier;
+
+        if (User.IsInRole("Admin"))
+        {
+            var feat = HttpContext.Features.Get<IExceptionHandlerPathFeature>();
+            AdminPath = feat?.Path;
+            if (feat?.Error is { } ex)
+                AdminDetail = ex.GetType().FullName + ": " + ex.Message
+                    + (ex.InnerException is { } ie ? $"\n  ↳ {ie.GetType().Name}: {ie.Message}" : "")
+                    + "\n\n" + ex.StackTrace;
+        }
     }
 }