feat: reboot button in Settings with password confirmation

- system.reboot RPC endpoint requires password re-verification
- Uses systemd path unit pattern (tor-helper.sh) for privilege escalation
- 2-second delay before reboot to allow RPC response to reach client
- Clean UI: password input modal, loading state, error feedback

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/tor-helper.sh

@@ -109,6 +109,13 @@ case "$ACTION_TYPE" in
     write_result '{"ok":true}'
     ;;
 
+  reboot)
+    write_result '{"ok":true}'
+    log "System reboot initiated"
+    sleep 1
+    systemctl reboot
+    ;;
+
   *)
     log "Unknown action: $ACTION_TYPE"
     write_result '{"ok":false,"error":"Unknown action"}'