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/winproto/noop.rs

@@ -0,0 +1,63 @@
+//! Port of apprt/gtk/winproto/noop.zig: used when neither X11 nor Wayland is
+//! detected.
+
+use std::rc::Rc;
+
+use gtk::gdk;
+
+use super::{Result, WindowHost};
+use ghostty_input::Mods;
+
+#[derive(Debug, Default, Clone, Copy)]
+pub struct App;
+
+impl App {
+    pub fn event_mods(&self, _: Option<&gdk::Device>, _: gdk::ModifierType) -> Option<Mods> {
+        None
+    }
+
+    pub fn supports_quick_terminal(&self) -> bool {
+        false
+    }
+
+    #[allow(clippy::unused_self, clippy::unnecessary_wraps)]
+    pub fn init_quick_terminal(&mut self, _: &gtk::Window) -> Result<()> {
+        Ok(())
+    }
+}
+
+#[derive(Debug, Default)]
+pub struct Window;
+
+impl Window {
+    #[allow(clippy::unnecessary_wraps)]
+    pub fn init(_: &App, _: Rc<dyn WindowHost>) -> Result<Window> {
+        Ok(Window)
+    }
+
+    #[allow(clippy::unused_self, clippy::unnecessary_wraps)]
+    pub fn resize_event(&mut self) -> Result<()> {
+        Ok(())
+    }
+
+    #[allow(clippy::unused_self, clippy::unnecessary_wraps)]
+    pub fn sync_appearance(&mut self) -> Result<()> {
+        Ok(())
+    }
+
+    /// Always true: this should be the actual present state of the window.
+    #[allow(clippy::unused_self)]
+    pub fn client_side_decoration_enabled(&self) -> bool {
+        true
+    }
+
+    #[allow(clippy::unused_self, clippy::unnecessary_wraps)]
+    pub fn add_subprocess_env(&mut self, _: &mut Vec<(String, String)>) -> Result<()> {
+        Ok(())
+    }
+
+    #[allow(clippy::unused_self, clippy::unnecessary_wraps)]
+    pub fn set_urgent(&mut self, _: bool) -> Result<()> {
+        Ok(())
+    }
+}