Implement Driftwood AppImage manager - Phases 1 and 2

Phase 1 - Application scaffolding:
- GTK4/libadwaita application window with AdwNavigationView
- GSettings-backed window state persistence
- GResource-compiled CSS and schema
- Library view with grid/list toggle, search, sorting, filtering
- Detail view with file info, desktop integration controls
- Preferences window with scan directories, theme, behavior settings
- CLI with list, scan, integrate, remove, clean, inspect commands
- AppImage discovery, metadata extraction, desktop integration
- Orphaned desktop entry detection and cleanup
- AppImage packaging script

Phase 2 - Intelligence layer:
- Database schema v2 with migration for status tracking columns
- FUSE detection engine (libfuse2/3, fusermount, /dev/fuse, AppImageLauncher)
- Wayland awareness engine (session type, toolkit detection, XWayland)
- Update info parsing from AppImage ELF sections (.upd_info)
- GitHub/GitLab Releases API integration for update checking
- Update download with progress tracking and atomic apply
- Launch wrapper with FUSE auto-detection and usage tracking
- Duplicate and multi-version detection with recommendations
- Dashboard with system health, library stats, disk usage
- Update check dialog (single and batch)
- Duplicate resolution dialog
- Status badges on library cards and detail view
- Extended CLI: status, check-updates, duplicates, launch commands

49 tests passing across all modules.

src/application.rs

@@ -0,0 +1,145 @@
+use adw::prelude::*;
+use adw::subclass::prelude::*;
+use gtk::gio;
+use std::cell::OnceCell;
+
+use crate::config::{APP_ID, VERSION};
+use crate::window::DriftwoodWindow;
+
+mod imp {
+    use super::*;
+
+    pub struct DriftwoodApplication {
+        pub settings: OnceCell<gio::Settings>,
+    }
+
+    impl Default for DriftwoodApplication {
+        fn default() -> Self {
+            Self {
+                settings: OnceCell::new(),
+            }
+        }
+    }
+
+    #[glib::object_subclass]
+    impl ObjectSubclass for DriftwoodApplication {
+        const NAME: &'static str = "DriftwoodApplication";
+        type Type = super::DriftwoodApplication;
+        type ParentType = adw::Application;
+    }
+
+    impl ObjectImpl for DriftwoodApplication {}
+
+    impl ApplicationImpl for DriftwoodApplication {
+        fn startup(&self) {
+            self.parent_startup();
+            let app = self.obj();
+            app.setup_css();
+            app.setup_theme();
+            app.setup_actions();
+        }
+
+        fn activate(&self) {
+            self.parent_activate();
+            let app = self.obj();
+
+            // Present existing window or create a new one
+            if let Some(window) = app.active_window() {
+                window.present();
+            } else {
+                let window = DriftwoodWindow::new(&*app);
+                window.present();
+            }
+        }
+    }
+
+    impl GtkApplicationImpl for DriftwoodApplication {}
+    impl AdwApplicationImpl for DriftwoodApplication {}
+}
+
+glib::wrapper! {
+    pub struct DriftwoodApplication(ObjectSubclass<imp::DriftwoodApplication>)
+        @extends adw::Application, gtk::Application, gio::Application,
+        @implements gio::ActionGroup, gio::ActionMap;
+}
+
+impl DriftwoodApplication {
+    pub fn new(app_id: &str, flags: &gio::ApplicationFlags) -> Self {
+        glib::Object::builder()
+            .property("application-id", app_id)
+            .property("flags", flags)
+            .build()
+    }
+
+    fn setup_css(&self) {
+        let provider = gtk::CssProvider::new();
+        provider.load_from_resource("/app/driftwood/Driftwood/style.css");
+        gtk::style_context_add_provider_for_display(
+            &gtk::gdk::Display::default().expect("Could not get default display"),
+            &provider,
+            gtk::STYLE_PROVIDER_PRIORITY_APPLICATION,
+        );
+    }
+
+    fn setup_theme(&self) {
+        let settings = gio::Settings::new(APP_ID);
+        Self::apply_color_scheme(&settings);
+
+        settings.connect_changed(Some("color-scheme"), |settings, _| {
+            Self::apply_color_scheme(settings);
+        });
+
+        // Store settings on the imp struct so it stays alive
+        // (otherwise the connect_changed signal gets dropped)
+        self.imp()
+            .settings
+            .set(settings)
+            .expect("Theme settings already initialized");
+    }
+
+    fn apply_color_scheme(settings: &gio::Settings) {
+        let value = settings.string("color-scheme");
+        let scheme = match value.as_str() {
+            "force-light" => adw::ColorScheme::ForceLight,
+            "force-dark" => adw::ColorScheme::ForceDark,
+            _ => adw::ColorScheme::Default,
+        };
+        adw::StyleManager::default().set_color_scheme(scheme);
+    }
+
+    fn setup_actions(&self) {
+        // Quit action (Ctrl+Q)
+        let quit_action = gio::ActionEntry::builder("quit")
+            .activate(|app: &Self, _, _| {
+                if let Some(window) = app.active_window() {
+                    window.close();
+                }
+                app.quit();
+            })
+            .build();
+
+        // About action
+        let about_action = gio::ActionEntry::builder("about")
+            .activate(|app: &Self, _, _| {
+                app.show_about_dialog();
+            })
+            .build();
+
+        self.add_action_entries([quit_action, about_action]);
+        self.set_accels_for_action("app.quit", &["<Control>q"]);
+    }
+
+    fn show_about_dialog(&self) {
+        let dialog = adw::AboutDialog::builder()
+            .application_name("Driftwood")
+            .application_icon(APP_ID)
+            .version(VERSION)
+            .developer_name("Driftwood Contributors")
+            .license_type(gtk::License::Gpl30)
+            .comments("A modern AppImage manager for GNOME desktops")
+            .website("https://github.com/driftwood-app/driftwood")
+            .build();
+
+        dialog.present(self.active_window().as_ref());
+    }
+}