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/ui/preferences.rs

@@ -0,0 +1,157 @@
+use adw::prelude::*;
+use gtk::gio;
+
+use crate::config::APP_ID;
+
+pub fn show_preferences_dialog(parent: &impl IsA<gtk::Widget>) {
+    let dialog = adw::PreferencesDialog::new();
+    dialog.set_title("Preferences");
+
+    let settings = gio::Settings::new(APP_ID);
+
+    // --- General page ---
+    let general_page = adw::PreferencesPage::builder()
+        .title("General")
+        .icon_name("emblem-system-symbolic")
+        .build();
+
+    // Appearance group
+    let appearance_group = adw::PreferencesGroup::builder()
+        .title("Appearance")
+        .build();
+
+    let theme_row = adw::ComboRow::builder()
+        .title("Color Scheme")
+        .subtitle("Choose light, dark, or follow system preference")
+        .build();
+
+    let model = gtk::StringList::new(&["Follow System", "Light", "Dark"]);
+    theme_row.set_model(Some(&model));
+
+    let current = settings.string("color-scheme");
+    theme_row.set_selected(match current.as_str() {
+        "force-light" => 1,
+        "force-dark" => 2,
+        _ => 0,
+    });
+
+    let settings_clone = settings.clone();
+    theme_row.connect_selected_notify(move |row| {
+        let value = match row.selected() {
+            1 => "force-light",
+            2 => "force-dark",
+            _ => "default",
+        };
+        settings_clone.set_string("color-scheme", value).ok();
+    });
+
+    appearance_group.add(&theme_row);
+    general_page.add(&appearance_group);
+
+    // Scan Locations group
+    let scan_group = adw::PreferencesGroup::builder()
+        .title("Scan Locations")
+        .description("Directories to scan for AppImage files")
+        .build();
+
+    let dirs = settings.strv("scan-directories");
+    let dir_list_box = gtk::ListBox::new();
+    dir_list_box.add_css_class("boxed-list");
+    dir_list_box.set_selection_mode(gtk::SelectionMode::None);
+
+    for dir in &dirs {
+        add_directory_row(&dir_list_box, &dir, &settings);
+    }
+
+    scan_group.add(&dir_list_box);
+
+    // Add location button
+    let add_button = gtk::Button::builder()
+        .label("Add Location")
+        .build();
+    add_button.add_css_class("flat");
+
+    let settings_add = settings.clone();
+    let list_box_ref = dir_list_box.clone();
+    let dialog_weak = dialog.downgrade();
+    add_button.connect_clicked(move |_| {
+        let file_dialog = gtk::FileDialog::builder()
+            .title("Choose a directory")
+            .modal(true)
+            .build();
+
+        let settings_ref = settings_add.clone();
+        let list_ref = list_box_ref.clone();
+        let dlg = dialog_weak.upgrade();
+        // Get the root window as the transient parent for the file dialog
+        let parent_window: Option<gtk::Window> = dlg
+            .as_ref()
+            .and_then(|d| d.root())
+            .and_then(|r| r.downcast::<gtk::Window>().ok());
+        file_dialog.select_folder(
+            parent_window.as_ref(),
+            None::<&gio::Cancellable>,
+            move |result| {
+                if let Ok(file) = result {
+                    if let Some(path) = file.path() {
+                        let path_str = path.to_string_lossy().to_string();
+
+                        let mut current_dirs: Vec<String> = settings_ref
+                            .strv("scan-directories")
+                            .iter()
+                            .map(|s| s.to_string())
+                            .collect();
+
+                        if !current_dirs.contains(&path_str) {
+                            current_dirs.push(path_str.clone());
+                            let refs: Vec<&str> =
+                                current_dirs.iter().map(|s| s.as_str()).collect();
+                            settings_ref.set_strv("scan-directories", refs).ok();
+
+                            add_directory_row(&list_ref, &path_str, &settings_ref);
+                        }
+                    }
+                }
+            },
+        );
+    });
+
+    scan_group.add(&add_button);
+    general_page.add(&scan_group);
+
+    dialog.add(&general_page);
+    dialog.present(Some(parent));
+}
+
+fn add_directory_row(list_box: &gtk::ListBox, dir: &str, settings: &gio::Settings) {
+    let row = adw::ActionRow::builder()
+        .title(dir)
+        .build();
+
+    let remove_btn = gtk::Button::builder()
+        .icon_name("edit-delete-symbolic")
+        .valign(gtk::Align::Center)
+        .tooltip_text("Remove")
+        .build();
+    remove_btn.add_css_class("flat");
+
+    let list_ref = list_box.clone();
+    let settings_ref = settings.clone();
+    let dir_str = dir.to_string();
+    let row_ref = row.clone();
+    remove_btn.connect_clicked(move |_| {
+        let current_dirs: Vec<String> = settings_ref
+            .strv("scan-directories")
+            .iter()
+            .map(|s| s.to_string())
+            .filter(|s| s != &dir_str)
+            .collect();
+        let refs: Vec<&str> = current_dirs.iter().map(|s| s.as_str()).collect();
+        settings_ref.set_strv("scan-directories", refs).ok();
+
+        list_ref.remove(&row_ref);
+    });
+
+    row.add_suffix(&remove_btn);
+    list_box.append(&row);
+}