Modernize error page with user-friendly design

[Copilot]

Replaced the default ASP.NET error page with a modern, user-friendly design that matches the application's AdminLTE-inspired theme.

Changes

UI Improvements

• Centered card layout with error icon, replacing plain text display
• User-friendly messaging: "Oops! Something went wrong" instead of "Error."
• Action buttons: "Go to Home" and "Go Back" with SVG icons
• Request ID displayed in styled box for support reference
• Development mode section collapsed into separate card below main error

Configuration

• Support email now injectable via AppSettings:SupportEmail (defaults to support@example.com)
• Development info visibility auto-detects from IWebHostEnvironment.IsDevelopment()

Before/After

Before:

<h1 class="text-danger">Error.</h1>
<h2 class="text-danger">An error occurred while processing your request.</h2>

After:

<div class="card shadow-admin-lg">
    <div class="error-icon"><!-- SVG icon --></div>
    <h1>Oops! Something went wrong</h1>
    <p>We encountered an unexpected error...</p>
    <button class="btn btn-primary">Go to Home</button>
</div>

Screenshot

Tests

Updated ErrorPageTests.cs with assertions for new elements (action buttons, support email, visual structure).

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• f.feedz.io
  • Triggering command: /opt/hostedtoolcache/CodeQL/2.23.8/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp /opt/hostedtoolcache/CodeQL/2.23.8/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Error Page</issue_title>
<issue_description>update the /error page to have a nicer user friendly look</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Error Page #664

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