"Return to Default Size" implementation

Added support for "Return To Default Size"

macos/Sources/App/macOS/AppDelegate.swift

@@ -753,6 +753,16 @@ class AppDelegate: NSObject,
         quickController.toggle()
     }
 
+    @IBAction func returnToDefaultSize(_ sender: Any) {
+        guard let window = NSApp.keyWindow else { return }
+        let currentOrigin = window.frame.origin
+        let newFrame = NSRect(
+            origin: currentOrigin,
+            size: WindowConfig.defaultSize
+        )
+        window.setFrame(newFrame, display: true)
+    }
+
     /// Toggles visibility of all Ghosty Terminal windows. When hidden, activates Ghostty as the frontmost application
     @IBAction func toggleVisibility(_ sender: Any) {
         // If we have focus, then we hide all windows.
@@ -804,6 +814,10 @@ class AppDelegate: NSObject,
         }
     }
 
+    private enum WindowConfig {
+        static let defaultSize = CGSize(width: 800, height: 600)
+    }
+
     private struct ToggleVisibilityState {
         let hiddenWindows: [Weak<NSWindow>]
         let keyWindow: Weak<NSWindow>?
@@ -833,3 +847,23 @@ class AppDelegate: NSObject,
         }
     }
 }
+
+extension AppDelegate: NSMenuItemValidation {
+    func validateMenuItem(_ item: NSMenuItem) -> Bool {
+        switch item.action {
+        case #selector(returnToDefaultSize):
+            guard let focusedWindow = NSApp.keyWindow else {
+                return false
+            }
+            if focusedWindow.styleMask.contains(.fullScreen) {
+                return false
+            }
+            if focusedWindow.frame.size == WindowConfig.defaultSize {
+                return false
+            }
+            return true
+        default:
+            return true
+        }
+    }
+}