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/features/quick_terminal/space_behavior.rs

@@ -0,0 +1,37 @@
+//! `QuickTerminalSpaceBehavior.swift`: the `quick-terminal-space-behavior` value.
+
+/// `enum QuickTerminalSpaceBehavior`.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Default)]
+pub enum QuickTerminalSpaceBehavior {
+    Remain,
+    #[default]
+    Move,
+}
+
+impl QuickTerminalSpaceBehavior {
+    /// `init?(fromGhosttyConfig:)`.
+    #[must_use]
+    pub fn from_ghostty_config(s: &str) -> Option<Self> {
+        match s {
+            "move" => Some(Self::Move),
+            "remain" => Some(Self::Remain),
+            _ => None,
+        }
+    }
+}
+
+#[cfg(target_vendor = "apple")]
+impl QuickTerminalSpaceBehavior {
+    /// `collectionBehavior`.
+    #[must_use]
+    pub fn collection_behavior(self) -> objc2_app_kit::NSWindowCollectionBehavior {
+        use objc2_app_kit::NSWindowCollectionBehavior as B;
+        let common = B::IgnoresCycle | B::FullScreenAuxiliary;
+        match self {
+            // We want this to move the window to the active space.
+            Self::Move => B::CanJoinAllSpaces | common,
+            // We want this to remain the window in the current space.
+            Self::Remain => B::MoveToActiveSpace | common,
+        }
+    }
+}