Add Reboot and Shutdown buttons to Settings page

POST /api/system/reboot → systemctl reboot
POST /api/system/shutdown → systemctl poweroff
Both require confirm() before executing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

audit/internal/webui/api.go

@@ -1292,6 +1292,22 @@ func (h *handler) handleAPIInstallToRAM(w http.ResponseWriter, r *http.Request)
 	_ = json.NewEncoder(w).Encode(map[string]string{"task_id": t.ID})
 }
 
+func (h *handler) handleAPISystemReboot(w http.ResponseWriter, r *http.Request) {
+	if err := exec.Command("systemctl", "reboot").Start(); err != nil {
+		writeError(w, http.StatusInternalServerError, "reboot failed: "+err.Error())
+		return
+	}
+	writeJSON(w, map[string]string{"status": "rebooting"})
+}
+
+func (h *handler) handleAPISystemShutdown(w http.ResponseWriter, r *http.Request) {
+	if err := exec.Command("systemctl", "poweroff").Start(); err != nil {
+		writeError(w, http.StatusInternalServerError, "shutdown failed: "+err.Error())
+		return
+	}
+	writeJSON(w, map[string]string{"status": "shutting down"})
+}
+
 // ── Tools ─────────────────────────────────────────────────────────────────────
 
 var standardTools = []string{