Revert build-generated copyright year in AssemblyInfo.cs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Vocaluxe/Properties/AssemblyInfo.cs

@@ -28,7 +28,7 @@ using System.Runtime.InteropServices;
 [assembly: AssemblyConfiguration("")]
 [assembly: AssemblyCompany("")]
 [assembly: AssemblyProduct("Vocaluxe")]
-[assembly: AssemblyCopyright("Copyright © 2026")]
+[assembly: AssemblyCopyright("Copyright © 2025")]
 [assembly: AssemblyTrademark("")]
 [assembly: AssemblyCulture("")]