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

iso/post-install.sh

@@ -0,0 +1,40 @@
+#!/bin/bash
+set -euo pipefail
+
+# --- Snapper root config ---
+snapper -c root create-config /
+sed -i 's/TIMELINE_CREATE="yes"/TIMELINE_CREATE="no"/' /etc/snapper/configs/root
+sed -i 's/NUMBER_CLEANUP="no"/NUMBER_CLEANUP="yes"/' /etc/snapper/configs/root
+sed -i 's/NUMBER_MIN_AGE="[^"]*"/NUMBER_MIN_AGE="1800"/' /etc/snapper/configs/root
+sed -i 's/NUMBER_LIMIT="[^"]*"/NUMBER_LIMIT="10"/' /etc/snapper/configs/root
+sed -i 's/NUMBER_LIMIT_IMPORTANT="[^"]*"/NUMBER_LIMIT_IMPORTANT="5"/' /etc/snapper/configs/root
+
+# Allow main user to use snapper without sudo
+MAIN_USER=$(getent passwd 1000 | cut -d: -f1)
+sed -i "s/ALLOW_USERS=\"\"/ALLOW_USERS=\"$MAIN_USER\"/" /etc/snapper/configs/root
+
+# --- System services ---
+systemctl enable NetworkManager
+systemctl enable bluetooth
+systemctl enable snapper-cleanup.timer
+systemctl enable grub-btrfs.path
+
+# --- Bakery install ---
+if command -v bakery &>/dev/null; then
+    sudo -u "$MAIN_USER" bakery install bread breadbar breadbox breadcrumbs breadpad bos-settings
+fi
+
+# --- Deploy dotfiles (skip existing files) ---
+DOTFILES_SRC="/etc/skel/.config"
+DOTFILES_DEST="/home/$MAIN_USER/.config"
+
+if [[ -d "$DOTFILES_SRC" ]]; then
+    mkdir -p "$DOTFILES_DEST"
+    cp -rn "$DOTFILES_SRC/." "$DOTFILES_DEST/"
+    chown -R "$MAIN_USER:$MAIN_USER" "$DOTFILES_DEST"
+fi
+
+# --- XDG user dirs ---
+sudo -u "$MAIN_USER" xdg-user-dirs-update
+
+echo "BOS post-install complete. Reboot to start your system."