feat(portal): M2b-3 note — enabled alerts keep the device monitored 24/7

UI note on the SLM alerts card reflecting the SLMM keepalive coupling.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

templates/slm_detail.html

@@ -120,7 +120,7 @@
             <h2 class="text-xl font-semibold text-gray-900 dark:text-white flex items-center gap-2">Alerts
                 <span id="alert-state-badge" class="hidden text-xs px-2 py-0.5 rounded-full"></span>
             </h2>
-            <p class="text-xs text-gray-500 dark:text-gray-400">Threshold rules evaluated on this device's live feed.</p>
+            <p class="text-xs text-gray-500 dark:text-gray-400">Threshold rules evaluated on this device's live feed. An enabled alert keeps the device monitored 24/7.</p>
         </div>
         <button onclick="openAlertForm()" type="button"
                 class="px-3 py-1.5 text-sm rounded-lg bg-seismo-orange text-white hover:bg-orange-600">+ Add alert</button>