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-capi-consts.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+"""Generate crates/ghostty-macos/src/ghostty/capi/consts.rs from
+crates/ghostty-lib/include/ghostty.h: every enumerator becomes a
+`pub const NAME: c_int` (the header's enums are C `int`s)."""
+import re, sys, pathlib
+root = pathlib.Path(__file__).resolve().parent.parent
+hdr = (root / "crates/ghostty-lib/include/ghostty.h").read_text()
+hdr = re.sub(r"/\*.*?\*/", "", hdr, flags=re.S)
+hdr = re.sub(r"//[^\n]*", "", hdr)
+out = [
+    "//! GENERATED by scripts/gen-macos-capi-consts.py from include/ghostty.h; do not edit.",
+    "//!",
+    "//! The enumerators of every C enum of the header (all `int`).",
+    "#![allow(missing_docs)]",
+    "",
+    "use std::ffi::c_int;",
+    "",
+]
+for m in re.finditer(r"typedef\s+enum\s*(?:\w+\s*)?\{(.*?)\}\s*(\w+)\s*;", hdr, flags=re.S):
+    body, name = m.group(1), m.group(2)
+    out.append(f"// {name}")
+    nxt = 0
+    for item in [x.strip() for x in body.split(",") if x.strip()]:
+        if "=" in item:
+            n, v = [x.strip() for x in item.split("=", 1)]
+            v = v.replace("UL", "").replace("U", "")
+            nxt = eval(v)
+        else:
+            n = item
+        out.append(f"pub const {n}: c_int = {nxt};")
+        nxt += 1
+    out.append("")
+sys.stdout.write("\n".join(out))