Publish GS2Engine packages to private feed

Changed:
- Update GS2Engine package copyright metadata through 2026.

Added:
- Publish release packages to the private Preagonal NuGet feed from Jenkins using its dedicated credential.
- Report successful private-feed publication through the existing Discord build notification.

Author: xx-shitai-xx

Jenkinsfile

@@ -177,6 +177,10 @@ def buildStepDocker() {
 							''');
 							discordSend description: "NuGet Successful", footer: "", link: env.BUILD_URL, result: currentBuild.currentResult, title: "[${split_job_name[0]}] Artifact Successful: ${fixed_job_name} #${env.BUILD_NUMBER}", webhookURL: env.GS2EMU_WEBHOOK;
 						}
+						withCredentials([string(credentialsId: 'PREAGONAL_PRIVATE_NUGET_TOKEN', variable: 'NUGET_TOKEN')]) {
+							sh("dotnet nuget push --skip-duplicate -s https://packages.preagonal.net/nuget/ -k ${env.NUGET_TOKEN} Preagonal.Scripting.GS2Engine/bin/Release/*.nupkg;chmod 777 -R .");
+							discordSend description: "NuGet Successful", footer: "", link: env.BUILD_URL, result: currentBuild.currentResult, title: "[${split_job_name[0]}] Artifact Successful: ${fixed_job_name} #${env.BUILD_NUMBER}", webhookURL: env.GS2EMU_WEBHOOK;
+						}
 						withCredentials([string(credentialsId: 'PREAGONAL_NUGET_TOKEN', variable: 'NUGET_TOKEN')]) {
 							sh('''
 								trap 'chmod 777 -R .' EXIT
@@ -324,4 +328,4 @@ node('master') {
 	}
 
 	sh("rm -rf ./*");
-}
+}

Preagonal.Scripting.GS2Engine/Preagonal.Scripting.GS2Engine.csproj

@@ -7,7 +7,7 @@
 		<LangVersion>latest</LangVersion>
 		<Title>GS2Engine</Title>
 		<Authors>Preagonal</Authors>
-		<Copyright>Preagonal 2023-2024</Copyright>
+		<Copyright>Preagonal 2023-2026</Copyright>
 		<PackageProjectUrl>https://github.com/Preagonal/GS2Engine</PackageProjectUrl>
 		<RepositoryUrl>https://github.com/Preagonal/GS2Engine</RepositoryUrl>
 		<AssemblyVersion>1.0.0</AssemblyVersion>