Scaffold BOS repo: dotfiles, ISO profile, and bos-settings GTK4 app

Implements all four components from the BOS spec:
- dotfiles/: default Hyprland, bread, breadbox, breadcrumbs configs
- iso/: archiso profiledef, package list, Calamares YAML modules, post-install.sh
- bos-settings/: Cargo workspace with GTK4 settings app (8 views: snapshots,
  packages, bread, breadbar, breadbox, breadcrumbs, breadpad, hyprland)

https://claude.ai/code/session_01WszGHvCmxgcyTwNSkfLF9P

bos-settings/src/ui/window.rs

@@ -0,0 +1,57 @@
+use gtk4::prelude::*;
+use gtk4::{Application, ApplicationWindow, Box as GBox, Orientation, Paned, Stack};
+
+use super::sidebar;
+use super::views;
+
+pub fn build_ui(app: &Application) {
+    let window = ApplicationWindow::builder()
+        .application(app)
+        .title("BOS Settings")
+        .default_width(960)
+        .default_height(640)
+        .build();
+
+    crate::theme::load(&window.display());
+
+    let hpaned = Paned::new(Orientation::Horizontal);
+    hpaned.set_position(190);
+    hpaned.set_shrink_start_child(false);
+    hpaned.set_resize_start_child(false);
+
+    let (sidebar_box, list) = sidebar::build();
+
+    let stack = Stack::new();
+    stack.set_hexpand(true);
+    stack.set_vexpand(true);
+
+    stack.add_named(&views::snapshots::build(), Some("snapshots"));
+    stack.add_named(&views::packages::build(), Some("packages"));
+    stack.add_named(&views::bread::build(), Some("bread"));
+    stack.add_named(&views::breadbar::build(), Some("breadbar"));
+    stack.add_named(&views::breadbox::build(), Some("breadbox"));
+    stack.add_named(&views::breadcrumbs::build(), Some("breadcrumbs"));
+    stack.add_named(&views::breadpad::build(), Some("breadpad"));
+    stack.add_named(&views::hyprland::build(), Some("hyprland"));
+
+    // Default to snapshots view
+    stack.set_visible_child_name("snapshots");
+
+    {
+        let stack = stack.clone();
+        list.connect_row_selected(move |_, row| {
+            if let Some(row) = row {
+                let name = row.widget_name();
+                if !name.is_empty() {
+                    stack.set_visible_child_name(&name);
+                }
+            }
+        });
+    }
+
+    hpaned.set_start_child(Some(&sidebar_box));
+    hpaned.set_end_child(Some(&stack));
+
+    window.set_child(Some(&hpaned));
+    window.present();
+}