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

scripts/gen-macos-menu-spec.py

@@ -0,0 +1,98 @@
+#!/usr/bin/env python3
+"""Generate the data tables of crates/ghostty-macos/src/app/menu_spec/generated.rs
+from Sources/App/macOS/MainMenu.xib of the Swift app (no ibtool needed).
+Usage: scripts/gen-macos-menu-spec.py [path/to/MainMenu.xib] > generated.rs"""
+import sys, pathlib
+import xml.etree.ElementTree as ET
+
+root = pathlib.Path(__file__).resolve().parent.parent
+default = root.parent / "ghostty/macos/Sources/App/macOS/MainMenu.xib"
+xib = pathlib.Path(sys.argv[1]) if len(sys.argv) > 1 else default
+r = ET.parse(xib).getroot()
+
+ids = {}  # object id -> customObject class
+for c in r.find("objects").findall("customObject"):
+    ids[c.get("id")] = c.get("customClass")
+outlets = {}  # menuItem id -> property
+for c in r.find("objects").findall("customObject"):
+    for o in c.iter("outlet"):
+        if o.get("property", "").startswith("menu"):
+            outlets[o.get("destination")] = o.get("property")
+used = []
+
+def camel(p):
+    return p[0].upper() + p[1:]
+
+def rs(s):
+    return '"' + s.replace("\\", "\\\\").replace('"', '\\"') + '"'
+
+def mods(item):
+    m = item.find("modifierMask")
+    if m is None:
+        return "None"  # IB default: command
+    parts = [n for n in ("shift", "control", "option", "command") if m.get(n) == "YES"]
+    if not parts:
+        return "Some(Mods::NONE)"
+    return "Some(Mods(" + " | ".join("Mods::" + p.upper() + ".0" for p in parts) + "))"
+
+def target(t):
+    if t == "-1":
+        return "Target::FirstResponder"
+    if t == "bbz-4X-AYv":
+        return "Target::AppDelegate"
+    raise SystemExit("unknown target " + str(t))
+
+def menu(m, ind):
+    pad = "    " * ind
+    sysm = {"apple": "Some(SystemMenu::Apple)", "window": "Some(SystemMenu::Window)",
+            "help": "Some(SystemMenu::Help)", "main": "Some(SystemMenu::Main)"}.get(m.get("systemMenu"), "None")
+    mo = outlets.get(m.get("id"))
+    if mo:
+        used.append(mo)
+    mo = ("Some(Outlet::" + camel(mo) + ")") if mo else "None"
+    out = [f"MenuSpec {{ title: {rs(m.get('title'))}, system_menu: {sysm}, outlet: {mo}, items: &["]
+    items = m.find("items")
+    for i in (items.findall("menuItem") if items is not None else []):
+        if i.get("isSeparatorItem") == "YES":
+            out.append(f"{pad}    ItemSpec::Separator,")
+            continue
+        act = i.find("connections/action")
+        action = "None"
+        if act is not None:
+            action = f"Some(Action {{ selector: {rs(act.get('selector'))}, target: {target(act.get('target'))} }})"
+        outlet = outlets.get(i.get("id"))
+        if outlet:
+            used.append(outlet)
+        sub = i.find("menu")
+        out.append(f"{pad}    ItemSpec::Item(Item {{")
+        out.append(f"{pad}        title: {rs(i.get('title'))},")
+        out.append(f"{pad}        key_equivalent: {rs(i.get('keyEquivalent', ''))},")
+        out.append(f"{pad}        modifiers: {mods(i)},")
+        out.append(f"{pad}        action: {action},")
+        out.append(f"{pad}        outlet: {('Some(Outlet::' + camel(outlet) + ')') if outlet else 'None'},")
+        if sub is not None:
+            out.append(f"{pad}        submenu: Some(&" + menu(sub, ind + 2) + "),")
+        else:
+            out.append(f"{pad}        submenu: None,")
+        out.append(f"{pad}    }}),")
+    out.append(f"{pad}] }}")
+    return "\n".join(out)
+
+top = r.find("objects").find("menu")
+body = menu(top, 1)
+print("//! GENERATED by scripts/gen-macos-menu-spec.py from MainMenu.xib; do not edit.")
+print("//!")
+print("//! Every menu item of the xib: title, key equivalent, modifier mask, action")
+print("//! selector + target (`-1` first responder / the AppDelegate) and the AppDelegate")
+print("//! outlet it is connected to.")
+print()
+print("use super::{Action, Item, ItemSpec, MenuSpec, Mods, Outlet, SystemMenu, Target};")
+print()
+print("/// The main menu (`systemMenu=\"main\"`).")
+print("pub const MAIN_MENU: MenuSpec = " + body + ";")
+print()
+print("/// All outlets connected in the xib (the Swift names).")
+print("pub const CONNECTED_OUTLETS: &[Outlet] = &[")
+for o in sorted(set(used)):
+    print(f"    Outlet::{camel(o)},")
+print("];")