feat(apprt-gtk): port the GTK4/libadwaita app runtime

Ports ZIG/src/apprt/gtk into ghostty-apprt-gtk: every GObject class
(application, window, tab, split tree, surface + scrolled window,
child-exited banner, search/key-state/resize overlays, command palette,
global shortcuts, all dialogs, config wrapper) as glib subclasses with
the same GType names, properties, signals and template children; GDK
key translation; X11 and Wayland window-protocol helpers (blur, CSD,
quick terminal via gtk4-layer-shell); single-instance D-Bus IPC;
gsettings; cgroup scope creation.

build.rs compiles Ghostty's blueprints with blueprint-compiler and
bundles UI, CSS and icons into a gresource, as Ghostty's build does.

The core is not ported yet, so the crate defines the boundary it needs
in src/core.rs (CoreApp, CoreSurface, RtApp, RtSurface, Waker); the
spec is in docs/rewrite/notes/ghostty-apprt-gtk.md. ghostty-core will
implement these traits (the crate no longer depends on core to avoid a
cycle). examples/demo.rs runs the app with a dummy core that clears the
GLArea; it launches on Wayland without GTK criticals.

Stubs/open items: toggle_visibility, float_window, secure_input and
close_all_windows return false; inspector is a no-op; X11/Wayland
protocol code is untested against real compositors; gtk4-rs doesn't
expose the GLArea framebuffer id, so the renderer must query it.

Also registers ghostty-apprt and ghostty-cli in workspace.dependencies.

Test Plan:
- cargo test -p ghostty-apprt-gtk (36 tests)
- DEMO_QUIT_AFTER_MS=3000 cargo run -p ghostty-apprt-gtk --example demo

crates/ghostty-apprt-gtk/src/lib.rs

@@ -1 +1,47 @@
-//! ghostty-apprt-gtk: see docs/rewrite/ARCHITECTURE.md for the module map.
+//! ghostty-apprt-gtk: the Linux GTK4 + libadwaita application runtime
+//! (ZIG/src/apprt/gtk/*). See docs/rewrite/notes/ghostty-apprt-gtk.md.
+
+pub mod adw_version;
+pub mod app;
+pub mod cgroup;
+pub mod class;
+pub mod core;
+pub mod css;
+pub mod ext;
+pub mod flatpak;
+pub mod gl;
+pub mod gsettings;
+pub mod gtk_version;
+pub mod ipc;
+pub mod key;
+pub mod post_fork;
+pub mod pre_exec;
+pub mod weak_ref;
+pub mod winproto;
+
+/// GTK application ID (Zig: `App.application_id`).
+pub const APPLICATION_ID: &str = if cfg!(debug_assertions) {
+    "com.mitchellh.ghostty-debug"
+} else {
+    "com.mitchellh.ghostty"
+};
+
+/// GTK object path (Zig: `App.object_path`).
+pub const OBJECT_PATH: &str = if cfg!(debug_assertions) {
+    "/com/mitchellh/ghostty_debug"
+} else {
+    "/com/mitchellh/ghostty"
+};
+
+/// Resource prefix of the bundled gresource.
+pub const RESOURCE_PREFIX: &str = "/com/mitchellh/ghostty";
+
+/// Register the compiled gresource bundle (UI files, CSS, icons). Must be
+/// called before any template class is instantiated. Idempotent.
+pub fn register_resources() {
+    static ONCE: std::sync::Once = std::sync::Once::new();
+    ONCE.call_once(|| {
+        gtk::gio::resources_register_include!("ghostty.gresource")
+            .expect("failed to register ghostty gresource");
+    });
+}