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/build.rs

@@ -0,0 +1,111 @@
+//! Compiles the blueprint UI files with `blueprint-compiler` and bundles them
+//! (plus CSS and icons) into a GResource, mirroring
+//! ZIG/src/apprt/gtk/build/{blueprint,gresource}.zig.
+
+#![allow(clippy::unwrap_used)]
+use std::fmt::Write as _;
+use std::path::{Path, PathBuf};
+use std::process::Command;
+
+const PREFIX: &str = "/com/mitchellh/ghostty";
+const APP_ID: &str = "com.mitchellh.ghostty";
+const ICON_SIZES: &[u32] = &[16, 32, 128, 256, 512, 1024];
+const CSS: &[&str] = &[
+    "style.css",
+    "style-dark.css",
+    "style-hc.css",
+    "style-hc-dark.css",
+];
+// (major, minor, name). The inspector / imgui blueprints are deferred.
+const BLUEPRINTS: &[(u32, u32, &str)] = &[
+    (1, 0, "clipboard-confirmation-dialog"),
+    (1, 4, "clipboard-confirmation-dialog"),
+    (1, 2, "close-confirmation-dialog"),
+    (1, 2, "config-errors-dialog"),
+    (1, 2, "debug-warning"),
+    (1, 3, "debug-warning"),
+    (1, 2, "resize-overlay"),
+    (1, 2, "search-overlay"),
+    (1, 2, "key-state-overlay"),
+    (1, 5, "split-tree"),
+    (1, 5, "split-tree-split"),
+    (1, 2, "surface"),
+    (1, 5, "surface-scrolled-window"),
+    (1, 3, "surface-child-exited"),
+    (1, 5, "tab"),
+    (1, 5, "title-dialog"),
+    (1, 5, "window"),
+    (1, 5, "command-palette"),
+];
+
+fn main() {
+    let manifest = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap());
+    let out = PathBuf::from(std::env::var("OUT_DIR").unwrap());
+    let res = manifest.join("resources");
+    println!("cargo:rerun-if-changed=resources");
+    println!("cargo:rerun-if-changed=build.rs");
+
+    let mut xml = String::new();
+    xml.push_str("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<gresources>\n");
+
+    let _ = writeln!(xml, "  <gresource prefix=\"{PREFIX}\">");
+    for name in CSS {
+        let _ = writeln!(
+            xml,
+            "    <file compressed=\"true\" alias=\"{name}\">css/{name}</file>"
+        );
+    }
+    xml.push_str("  </gresource>\n");
+
+    let _ = writeln!(xml, "  <gresource prefix=\"{PREFIX}/icons\">");
+    for &s in ICON_SIZES {
+        let _ = writeln!(
+            xml,
+            "    <file alias=\"{s}x{s}/apps/{APP_ID}.png\">icons/{s}.png</file>"
+        );
+        let _ = writeln!(
+            xml,
+            "    <file alias=\"{s}x{s}@2/apps/{APP_ID}.png\">icons/{}.png</file>",
+            s * 2
+        );
+    }
+    xml.push_str("  </gresource>\n");
+
+    let _ = writeln!(xml, "  <gresource prefix=\"{PREFIX}/ui\">");
+    for &(major, minor, name) in BLUEPRINTS {
+        let rel = format!("{major}.{minor}/{name}");
+        let input = res.join(format!("ui/{rel}.blp"));
+        let output = out.join(format!("ui/{rel}.ui"));
+        compile_blueprint(&input, &output);
+        let _ = writeln!(xml, "    <file alias=\"{rel}.ui\">ui/{rel}.ui</file>");
+    }
+    xml.push_str("  </gresource>\n</gresources>\n");
+
+    let xml_path = out.join("ghostty.gresource.xml");
+    std::fs::write(&xml_path, xml).unwrap();
+
+    glib_build_tools::compile_resources(
+        &[out.as_path(), res.as_path()],
+        xml_path.to_str().unwrap(),
+        "ghostty.gresource",
+    );
+}
+
+fn compile_blueprint(input: &Path, output: &Path) {
+    std::fs::create_dir_all(output.parent().unwrap()).unwrap();
+    let st = Command::new("blueprint-compiler")
+        .arg("compile")
+        .arg("--output")
+        .arg(output)
+        .arg(input)
+        .output()
+        .unwrap_or_else(|e| {
+            panic!("`blueprint-compiler` (>= 0.16) is required to build ghostty-apprt-gtk: {e}")
+        });
+    assert!(
+        st.status.success(),
+        "blueprint-compiler failed for {}:\n{}",
+        input.display(),
+        String::from_utf8_lossy(&st.stderr)
+    );
+}