feat: rewrite moonset in Rust (gtk4-rs + gtk4-layer-shell)

Feature-parity with Python v0.2.0. Same CSS, same UI, same actions.
Single 3.1 MB binary with embedded resources (CSS, wallpaper, avatar).

Modules: power.rs, i18n.rs, config.rs, users.rs, panel.rs, main.rs
45 unit tests passing. Python sources retained as reference.

src/main.rs

@@ -0,0 +1,90 @@
+// ABOUTME: Entry point for Moonset — Wayland session power menu.
+// ABOUTME: Sets up GTK Application, Layer Shell, CSS, and multi-monitor windows.
+
+mod config;
+mod i18n;
+mod panel;
+mod power;
+mod users;
+
+use gdk4 as gdk;
+use gtk4::prelude::*;
+use gtk4::{self as gtk, gio};
+use gtk4_layer_shell::LayerShell;
+
+fn load_css(display: &gdk::Display) {
+    let css_provider = gtk::CssProvider::new();
+    css_provider.load_from_resource("/dev/moonarch/moonset/style.css");
+    gtk::style_context_add_provider_for_display(
+        display,
+        &css_provider,
+        gtk::STYLE_PROVIDER_PRIORITY_APPLICATION,
+    );
+}
+
+fn setup_layer_shell(
+    window: &gtk::ApplicationWindow,
+    keyboard: bool,
+    layer: gtk4_layer_shell::Layer,
+) {
+    window.init_layer_shell();
+    window.set_layer(layer);
+    window.set_exclusive_zone(-1);
+    if keyboard {
+        window.set_keyboard_mode(gtk4_layer_shell::KeyboardMode::Exclusive);
+    }
+    // Anchor to all edges for fullscreen
+    window.set_anchor(gtk4_layer_shell::Edge::Top, true);
+    window.set_anchor(gtk4_layer_shell::Edge::Bottom, true);
+    window.set_anchor(gtk4_layer_shell::Edge::Left, true);
+    window.set_anchor(gtk4_layer_shell::Edge::Right, true);
+}
+
+fn activate(app: &gtk::Application) {
+    let display = match gdk::Display::default() {
+        Some(d) => d,
+        None => {
+            log::error!("No display available — cannot start power menu UI");
+            return;
+        }
+    };
+
+    load_css(&display);
+
+    // Resolve wallpaper once, share across all windows
+    let config = config::load_config(None);
+    let bg_path = config::resolve_background_path(&config);
+
+    // Panel on focused output (no set_monitor → compositor picks focused)
+    let panel = panel::create_panel_window(&bg_path, app);
+    setup_layer_shell(&panel, true, gtk4_layer_shell::Layer::Overlay);
+    panel.present();
+
+    // Wallpaper on all monitors
+    let monitors = display.monitors();
+    for i in 0..monitors.n_items() {
+        if let Some(monitor) = monitors.item(i).and_then(|obj| obj.downcast::<gdk::Monitor>().ok()) {
+            let wallpaper = panel::create_wallpaper_window(&bg_path, app);
+            setup_layer_shell(&wallpaper, false, gtk4_layer_shell::Layer::Top);
+            wallpaper.set_monitor(Some(&monitor));
+            wallpaper.present();
+        }
+    }
+}
+
+fn main() {
+    env_logger::Builder::from_default_env()
+        .filter_level(log::LevelFilter::Info)
+        .init();
+    log::info!("Moonset starting");
+
+    // Register compiled GResources
+    gio::resources_register_include!("moonset.gresource").expect("Failed to register resources");
+
+    let app = gtk::Application::builder()
+        .application_id("dev.moonarch.moonset")
+        .build();
+
+    app.connect_activate(activate);
+    app.run();
+}