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

app/sovran_systemsos_web/static/css/layout.css

@@ -84,6 +84,21 @@
   margin: 16px 0;
 }
 
+/* ── Sidebar restart button (amber/muted treatment) ─────────────── */
+
+.sidebar-restart-btn {
+  border-color: rgba(184, 125, 0, 0.25);
+}
+
+.sidebar-restart-btn:hover {
+  border-color: #b87d00;
+  background-color: rgba(184, 125, 0, 0.08);
+}
+
+.sidebar-restart-btn .sidebar-restart-hint {
+  color: #c98d08;
+}
+
 /* ── Upgrade modal ──────────────────────────────────────────────── */
 
 .upgrade-dialog {