macos: quit if we have no visible windows

macos/Sources/GhosttyApp.swift

@@ -120,6 +120,15 @@ class AppDelegate: NSObject, NSApplicationDelegate, ObservableObject {
     }
     
     func applicationShouldTerminate(_ sender: NSApplication) -> NSApplication.TerminateReply {
+        let windows = NSApplication.shared.windows
+        if (windows.isEmpty) { return .terminateNow }
+        
+        // This probably isn't fully safe. The isEmpty check above is aspirational, it doesn't
+        // quit work with SwiftUI because windows are retained on close. So instead we check
+        // if there are any that are visible. I'm guessing this breaks under certain scenarios.
+        if (windows.allSatisfy { !$0.isVisible }) { return .terminateNow }
+        
+        // We have some visible window, and all our windows will watch the confirmQuit.
         confirmQuit = true
         return .terminateLater
     }

macos/Sources/SettingsView.swift

@@ -1,6 +1,9 @@
 import SwiftUI
 
 struct SettingsView: View {
+    // We need access to our app delegate to know if we're quitting or not.
+    @EnvironmentObject private var appDelegate: AppDelegate
+    
     var body: some View {
         HStack {
             Image("AppIconImage")
@@ -18,6 +21,10 @@ struct SettingsView: View {
         }
         .padding()
         .frame(minWidth: 500, maxWidth: 500, minHeight: 156, maxHeight: 156)
+        .onChange(of: appDelegate.confirmQuit) { value in
+            guard value else { return }
+            NSApplication.shared.reply(toApplicationShouldTerminate: true)
+        }
     }
 }