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/helpers/extensions/ns_screen_logic.rs

@@ -0,0 +1,127 @@
+//! The platform independent parts of `Helpers/Extensions/NSScreen+Extension.swift`
+//! (and the Swift `NSScreenTests`).
+
+use crate::helpers::geometry::{Point, Rect, Size};
+
+/// `NSScreen.origin(fromTopLeftOffsetX:offsetY:windowSize:)`: converts
+/// top-left offset coordinates to bottom-left origin coordinates for window
+/// positioning, relative to the screen's `visibleFrame`.
+#[must_use]
+pub fn origin_from_top_left_offset(
+    visible_frame: Rect,
+    x: f64,
+    y: f64,
+    window_size: Size,
+) -> Point {
+    // Convert top-left coordinates to bottom-left origin
+    Point {
+        x: visible_frame.min_x() + x,
+        y: visible_frame.max_y() - y - window_size.height,
+    }
+}
+
+/// The geometry part of `NSScreen.hasDock` (after the autohide default check).
+#[must_use]
+pub fn has_visible_dock(
+    visible_frame: Rect,
+    frame: Rect,
+    menu_height: f64,
+    notch_inset: f64,
+) -> bool {
+    // If our visible width is less than the frame we assume its the dock.
+    if visible_frame.width() < frame.width() {
+        return true;
+    }
+
+    // We need to see if our visible frame height is less than the full
+    // screen height minus the menu and notch and such.
+    let boundary_area_padding = 5.0;
+    visible_frame.height() < (frame.height() - menu_height.max(notch_inset) - boundary_area_padding)
+}
+
+/// `NSScreen.hasNotch`: a top safe area inset is assumed to mean a notch.
+#[must_use]
+pub fn has_notch(safe_area_top: f64) -> bool {
+    safe_area_top > 0.0
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const WIN: Size = Size {
+        width: 400.0,
+        height: 300.0,
+    };
+
+    #[test]
+    fn positive_coordinate_conversion() {
+        let o = origin_from_top_left_offset(Rect::new(0.0, 100.0, 1000.0, 800.0), 15.0, 15.0, WIN);
+        assert_eq!((o.x, o.y), (15.0, 585.0));
+    }
+
+    #[test]
+    fn zero_coordinates() {
+        let o = origin_from_top_left_offset(Rect::new(0.0, 100.0, 1000.0, 800.0), 0.0, 0.0, WIN);
+        assert_eq!((o.x, o.y), (0.0, 600.0));
+    }
+
+    #[test]
+    fn offset_screen() {
+        let o = origin_from_top_left_offset(
+            Rect::new(1440.0, 0.0, 1920.0, 1080.0),
+            100.0,
+            50.0,
+            Size {
+                width: 600.0,
+                height: 400.0,
+            },
+        );
+        assert_eq!((o.x, o.y), (1540.0, 630.0));
+    }
+
+    #[test]
+    fn large_coordinates() {
+        let o = origin_from_top_left_offset(Rect::new(0.0, 0.0, 1920.0, 1080.0), 500.0, 200.0, WIN);
+        assert_eq!((o.x, o.y), (500.0, 580.0));
+    }
+
+    #[test]
+    fn dock_detection() {
+        let frame = Rect::new(0.0, 0.0, 1000.0, 800.0);
+        // side dock
+        assert!(has_visible_dock(
+            Rect::new(70.0, 0.0, 930.0, 776.0),
+            frame,
+            24.0,
+            0.0
+        ));
+        // bottom dock
+        assert!(has_visible_dock(
+            Rect::new(0.0, 70.0, 1000.0, 706.0),
+            frame,
+            24.0,
+            0.0
+        ));
+        // no dock, only menu bar
+        assert!(!has_visible_dock(
+            Rect::new(0.0, 0.0, 1000.0, 776.0),
+            frame,
+            24.0,
+            0.0
+        ));
+        // notch inset larger than the menu
+        assert!(!has_visible_dock(
+            Rect::new(0.0, 0.0, 1000.0, 760.0),
+            frame,
+            24.0,
+            38.0
+        ));
+    }
+
+    #[test]
+    fn notch() {
+        assert!(has_notch(32.0));
+        assert!(!has_notch(0.0));
+    }
+}