feat: gate first limited Apply pilot

Launcher.Next.Core/Contracts.cs

@@ -1,7 +1,7 @@
 namespace Launcher.Next.Core;
 
 public enum LauncherMode { Legacy, DryRun, NextPilot, NextPreferred }
-public enum PluginExecutionMode { Smoke, DryRun }
+public enum PluginExecutionMode { Smoke, DryRun, Apply }
 public sealed record ProductInstallation(string ExecutablePath, string ProductVersion, string Architecture, IReadOnlyList<string> Profiles);
 public sealed record PackageFile(string Path, long Length, string Sha256, bool Optional = false);
 public sealed record StartupDefinition(string Type, string Command);