bos-settings 0.6.0: Power, Firewall, Users, AUR, Firmware panels

Continues reducing terminal-reliance for graphical system control. Five
new panels, plus three GUI apps shipped for things better served by an
existing dedicated tool than reimplemented in bos-settings
(gnome-disk-utility, gufw, mission-center).

- Power: battery status/health, brightness, charge-limit thresholds where
  the hardware exposes them, TLP profile shown read-only by design (no
  Balanced/Performance switcher — TLP auto-selects by power source, and
  power-profiles-daemon isn't installed because it conflicts with tlp).
- Firewall: ufw enable/disable, add/remove rules, view active rules.
  ufw's own status check requires root (confirmed against the installed
  script — not just changes, reads too), so unlike every other panel this
  one does NOT query state in build(): every view is constructed eagerly
  at app launch, and an unconditional privileged read here would mean a
  polkit prompt on every single bos-settings open. Starts blank with a
  "Status not loaded" placeholder; state loads only on an explicit Refresh
  click, with a guard so refresh's own set_active() doesn't loop back into
  triggering ufw enable/disable.
- Users: add/remove accounts, change passwords. All through pkexec on a
  background thread. Can't remove the account you're currently running as.
- AUR: search via yay. Installing deliberately opens a terminal instead of
  a silent --noconfirm install — yay's interactive PKGBUILD diff review and
  sudo prompt are the actual safety mechanism against a malicious AUR
  package, not a formality worth automating away.
- Firmware: fwupd device list + updates, same stream-output-then-refresh
  pattern as Packages.

packages.x86_64: gnome-disk-utility, gufw, mission-center for disk/firewall/
task-manager GUIs that don't need reinventing inside bos-settings.

bos-settings/src/ui/window.rs

@@ -35,8 +35,13 @@ pub fn build_ui(app: &Application) {
     stack.add_named(&views::network::build(), Some("network"));
     stack.add_named(&views::sound::build(), Some("sound"));
     stack.add_named(&views::datetime::build(), Some("datetime"));
+    stack.add_named(&views::power::build(), Some("power"));
+    stack.add_named(&views::firewall::build(), Some("firewall"));
+    stack.add_named(&views::users::build(), Some("users"));
     stack.add_named(&views::snapshots::build(), Some("snapshots"));
     stack.add_named(&views::packages::build(), Some("packages"));
+    stack.add_named(&views::firmware::build(), Some("firmware"));
+    stack.add_named(&views::aur::build(), Some("aur"));
     stack.add_named(&views::bread::build(), Some("bread"));
     stack.add_named(&views::breadbar::build(), Some("breadbar"));
     stack.add_named(&views::breadbox::build(), Some("breadbox"));