feat: implement consistent restart UX across Sovran_SystemsOS Hub

- Add Restart Entire System sidebar action with amber treatment and divider
- Add shared restart confirmation dialog with conflict detection
- Update reboot overlay: new title, body copy, status progression, error card
- Improve doReboot(): failure handling, aria-live status messages
- Standardize 'restart required' / 'Restart Entire System' terminology
- Update security.js reboot flow to use shared doReboot()
- Update installer.py button label
- Add .btn-restart-amber, .restart-conflict-box, .sidebar-restart-btn CSS

iso/installer.py

@@ -1169,7 +1169,7 @@ class InstallerWindow(Adw.ApplicationWindow):
         btn_box = Gtk.Box(orientation=Gtk.Orientation.HORIZONTAL, spacing=0)
         btn_box.set_halign(Gtk.Align.CENTER)
         btn_box.set_margin_bottom(32)
-        reboot_btn = Gtk.Button(label="I Have Written Down My Password — Reboot Now")
+        reboot_btn = Gtk.Button(label="I Have Written Down My Password — Restart Entire System")
         reboot_btn.add_css_class("suggested-action")
         reboot_btn.add_css_class("pill")
         reboot_btn.connect("clicked", lambda b: subprocess.run(["sudo", "reboot"]))