feat(macos): port Ghostty's macOS code paths (Metal, CoreText, Darwin)

Ports the macOS-specific Zig code behind cfg(target_os = "macos"):
- renderer: a GraphicsApi trait with generic::Renderer<G>; Metal backend
  (all renderer/metal/* files, shaders.metal verbatim, runtime library
  compile, IOSurface layer, CVDisplayLink), shadertoy -> MSL via naga;
  OpenGL remains the backend elsewhere.
- font: CoreText face, shaper and discovery with build.rs backend
  selection (coretext default; coretext-freetype / coretext-harfbuzz /
  coretext-noshape features), no fontconfig/freetype/harfbuzz on Apple.
- input: KeymapDarwin via UCKeyTranslate, option-as-alt, mac keycodes.
- os: macos, mach, cf_release_thread, NSProcessInfo args and macOS
  branches; config: macOS defaults, keybinds, Application Support paths.
- termio/core: login(1) wrapping, openpty/execvpe, Darwin child exit
  handling, os_log logging.

Compile-checked for aarch64/x86_64-apple-darwin (clippy -D warnings
clean) using the cross setup in docs/rewrite/notes/macos-M1.md; cannot
run here. The embedded runtime/C API (embedded.zig) is the next step.

Also includes the cross-platform integration edits shared by the crash,
verification, Windows and macOS work (Cargo target-gating, thread
crash-context hooks, apprt-gtk surface/IME refactor, termio/os cfg
gates), a cfg fix so ghostty-config builds on wasm32, and an allow for
the intentional recursion in the crash overflow test.

Test Plan:
- cargo test --workspace (3224 passed)
- cargo clippy --workspace --all-targets -- -D warnings
- cargo check --target aarch64-apple-darwin -p ghostty-renderer (with
  the documented cross env)

crates/ghostty-os/src/resourcesdir.rs

@@ -29,8 +29,21 @@ impl ResourcesDir {
 
 /// Sentinels we look for in the path to know we've found the resources
 /// directory (Linux).
+#[cfg(not(any(windows, target_os = "macos")))]
 const SENTINELS: [&str; 2] = ["terminfo/g/ghostty", "terminfo/x/xterm-ghostty"];
 
+/// Sentinel on macOS (terminfo directories are named by hex there).
+#[cfg(target_os = "macos")]
+const SENTINELS: [&str; 1] = ["terminfo/78/xterm-ghostty"];
+
+/// Sentinel on Windows (a single terminfo source file).
+#[cfg(windows)]
+const SENTINELS: [&str; 1] = ["terminfo/ghostty.terminfo"];
+
+/// The in-repo `resources/` tree always carries the Linux-style terminfo
+/// layout (also on macOS, where the installed layout uses hex dirs).
+const DEV_SENTINELS: [&str; 1] = ["terminfo/x/xterm-ghostty"];
+
 /// Gets the directory to the bundled resources directory, if it
 /// exists (not all platforms or packages have it).
 ///
@@ -71,6 +84,17 @@ fn resources_dir_impl(debug: bool, exe: Option<&Path>, env: Option<String>) -> R
         exe = dir;
         let dir_str = dir.to_string_lossy();
 
+        // On MacOS, we look for the app bundle path.
+        #[cfg(target_vendor = "apple")]
+        for sentinel in SENTINELS {
+            if let Some(v) = maybe_dir(&dir_str, "Contents/Resources", sentinel) {
+                return ResourcesDir {
+                    app_path: Some(path_join(&[&v, "ghostty"])),
+                    host_path: None,
+                };
+            }
+        }
+
         // We look for a /usr/share style path.
         for sentinel in SENTINELS {
             if let Some(v) = maybe_dir(&dir_str, "share", sentinel) {
@@ -122,6 +146,7 @@ fn dev_resources_dir(exe: &Path) -> Option<String> {
     let res = root.join("resources");
     SENTINELS
         .iter()
+        .chain(DEV_SENTINELS.iter())
         .any(|s| res.join(s).exists())
         .then(|| res.to_string_lossy().into_owned())
 }
@@ -142,7 +167,7 @@ pub fn maybe_dir(base: &str, sub: &str, suffix: &str) -> Option<String> {
     None
 }
 
-#[cfg(test)]
+#[cfg(all(test, unix))]
 mod tests {
     use super::*;