feat(macos): foundation of the macOS app ported from Swift to Rust

Phase 9, MA1: crates/ghostty-macos (AppKit via objc2; empty stub on
non-Apple targets) ports the foundation of Ghostty 1.3.1's Swift macOS
app (ghostty/macos): main, AppDelegate (+Ghostty) with lifecycle, dock
menu, open-file, notifications, shortcut sync and quit/reopen paths;
MainMenu.xib as generated menu tables built into NSMenus; the
Ghostty.App/Config/Surface wrappers driving libghostty in-process via
ghostty-lib; the generic helpers; scripts/macos-bundle.sh to assemble
Ghostty.app (dry-run on Linux). Feature areas are stubbed for MA2-MA5.
Design and type mapping: docs/rewrite/notes/macos-app-design.md
(App Intents is a Swift-only framework and cannot be ported).

Compile-checked only (no macOS here): just check-macos passes for
aarch64/x86_64-apple-darwin with -D warnings; 125 platform-independent
tests run on Linux.

Test Plan:
- just check-macos
- cargo test -p ghostty-macos

crates/ghostty-macos/src/app/app_delegate_ghostty.rs

@@ -0,0 +1,33 @@
+//! `AppDelegate+Ghostty.swift`: the Ghostty app delegate protocol
+//! (`Ghostty.Delegate`), used by the libghostty glue for app-global
+//! information.
+
+use objc2::{MainThreadOnly, rc::Retained};
+use objc2_app_kit::NSApplication;
+use objc2_foundation::{NSObjectProtocol, NSUUID};
+
+use super::app_delegate::AppDelegate;
+use crate::{features::terminal::BaseTerminalController, ghostty::surface_view::SurfaceView};
+
+impl AppDelegate {
+    /// `ghosttySurface(id:)`: find a surface view by its id in any terminal window.
+    #[must_use]
+    pub fn ghostty_surface(&self, id: &NSUUID) -> Option<Retained<SurfaceView>> {
+        for window in NSApplication::sharedApplication(self.mtm()).windows() {
+            let Some(controller) = window
+                .windowController()
+                .and_then(|c| c.downcast::<BaseTerminalController>().ok())
+            else {
+                continue;
+            };
+
+            for surface in controller.surface_tree() {
+                if surface.id().isEqual(Some(id)) {
+                    return Some(surface);
+                }
+            }
+        }
+
+        None
+    }
+}