Fix VM window not appearing on tart run

Restore the applicationDidFinishLaunching method that was accidentally
removed in commit b1e88e1 ("tart run: do not remove 'Edit' menu as its
not present anymore").

That commit intended to remove the Edit menu removal code (since the
menu no longer exists), but also removed the crucial activation code:
- setActivationPolicy(.regular) - tells macOS this is a GUI app
- activate(ignoringOtherApps:) - brings the window to the foreground

Without these calls, the VM runs fine (SSH works) but no window appears
on screen.

Fixes #1181

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Sources/tart/Commands/Run.swift

@@ -819,6 +819,12 @@ struct MainApp: App {
 }
 
 class AppDelegate: NSObject, NSApplicationDelegate, ObservableObject {
+  func applicationDidFinishLaunching(_ : Notification) {
+    let nsApp = NSApplication.shared
+    nsApp.setActivationPolicy(.regular)
+    nsApp.activate(ignoringOtherApps: true)
+  }
+
   func applicationShouldTerminate(_ sender: NSApplication) -> NSApplication.TerminateReply {
     if (kill(getpid(), MainApp.suspendable ? SIGUSR1 : SIGINT) == 0) {
       return .terminateLater