macos: in new_window action, activate App

This change makes sure that the new window is focused and visible.

When commit 33d128bcff removed the
TerminalManager class and moved its functionality into
TerminalController, it accidentally removed app activation for windows
triggered by global keybinds.

How the bug works:

   1. Menu actions (like File → New Window) call AppDelegate.newWindow()
      which:
      2. Calls TerminalController.newWindow()
      3. AND explicitly calls NSApp.activate(ignoringOtherApps: true) in
         the AppDelegate
   4. Global keybind actions trigger ghosttyNewWindow() notification
      handler which:
      5. Only calls TerminalController.newWindow()
      6. Does NOT call NSApp.activate(ignoringOtherApps: true)
   7. While TerminalController.newWindow() does call
      NSApp.activate(ignoringOtherApps: true) internally, this call
      happens before the async dispatch that shows the window, so the
      activation occurs but the window isn't focused when it's actually
      shown.
   8. In the old TerminalManager.newWindow(), the activation happened
      immediately before the async dispatch, ensuring proper timing for
      window focus.

The fix would be to either move the NSApp.activate() call back into
TerminalController.newWindow(), as it was for TerminalManager, or add
the activation call to the notification handlers in AppDelegate.

macos/Sources/Features/Terminal/TerminalController.swift

@@ -214,6 +214,10 @@ class TerminalController: BaseTerminalController, TabGroupCloseCoordinator.Contr
             }
         }
 
+        // All new_window actions force our app to be active, so that the new
+        // window is focused and visible.
+        NSApp.activate(ignoringOtherApps: true)
+
         // We're dispatching this async because otherwise the lastCascadePoint doesn't
         // take effect. Our best theory is there is some next-event-loop-tick logic
         // that Cocoa is doing that we need to be after.