Update deps, docs, auth logic; add SixLabors license

- Expanded copilot-instructions.md with project/routing details and ImageSharp license handling
- Upgraded MailKit and MimeKit to v4.17.0
- Added sixlabors.lic for ImageSharp 4.x licensing
- Removed SecretManagementExtensions.cs stub
- Updated OCORE and OCORE_web submodules
- Improved unauthorized access handling in IntranetController
- Removed empty placeholder file

Fuchs/Services/SecretManagementExtensions.cs

@@ -1,16 +0,0 @@
-using Microsoft.AspNetCore.Builder;
-
-namespace OCORE_web.Secrets;
-
-/// <summary>
-/// Placeholder for secret management extension methods.
-/// Replace with a real Azure Key Vault / DPAPI implementation when ready.
-/// </summary>
-public static class SecretManagementExtensions
-{
-    /// <summary>
-    /// No-op stub. Wire up real secret management (e.g. Azure Key Vault) here.
-    /// </summary>
-    public static WebApplicationBuilder AddSecretManagement(this WebApplicationBuilder builder)
-        => builder;
-}