macOS: implement move_tab_to_new_window (#14216)

Closes #2630 for macOS. #13621 added the `move_tab_to_new_window` action
and the GTK side; this does the same on macOS with AppKit.

With native tabs a tab is already a window, so the action forwards to
AppKit's own `moveTabToNewWindow:`. It's a no-op when the window is
alone in its tab group, same as the Window menu item. The "only
implemented on Linux" note comes off the doc comment in `Binding.zig`.
Tested on macOS 26, from a keybind and from the command palette. I have
no macOS 13-15 machine.

Full disclosure, written with Claude Code, I directed it, read every
line, and tested the result.

macos/Sources/Ghostty/Ghostty.App.swift

@@ -621,6 +621,9 @@ extension Ghostty {
             case GHOSTTY_ACTION_MOVE_TAB:
                 return moveTab(app, target: target, move: action.action.move_tab)
 
+            case GHOSTTY_ACTION_MOVE_TAB_TO_NEW_WINDOW:
+                return moveTabToNewWindow(app, target: target)
+
             case GHOSTTY_ACTION_GOTO_TAB:
                 return gotoTab(app, target: target, tab: action.action.goto_tab)
 
@@ -1278,6 +1281,31 @@ extension Ghostty {
                 return true
         }
 
+        private static func moveTabToNewWindow(
+            _ app: ghostty_app_t,
+            target: ghostty_target_s) -> Bool {
+                switch target.tag {
+                case GHOSTTY_TARGET_APP:
+                    Ghostty.logger.warning("move tab to new window does nothing with an app target")
+                    return false
+
+                case GHOSTTY_TARGET_SURFACE:
+                    guard let surface = target.target.surface else { return false }
+                    guard let surfaceView = self.surfaceView(from: surface) else { return false }
+
+                    // See gotoTab for notes on this check. A lone tab is already
+                    // a window of its own, so there is nothing to move.
+                    guard (surfaceView.window?.tabGroup?.windows.count ?? 0) > 1 else { return false }
+
+                    surfaceView.window?.moveTabToNewWindow(nil)
+
+                default:
+                    assertionFailure()
+                }
+
+                return true
+        }
+
         private static func gotoTab(
             _ app: ghostty_app_t,
             target: ghostty_target_s,

src/input/Binding.zig

@@ -588,9 +588,6 @@ pub const Action = union(enum) {
     move_tab: isize,
 
     /// Move a tab to a new window.
-    ///
-    /// Only implemented on Linux, but there's a native tab menu provided by
-    /// macOS.
     move_tab_to_new_window,
 
     /// Toggle the tab overview.