Phase 2: monitoring warnings, dashboard alerts & notification system

- Monitoring page: "Távoli monitoring" section showing healthcheck ping UUID
  configuration status (configured/not configured) for each of the 5 pings
- Alert manager: persistent dashboard banners on all pages generated from
  health check results, missing pings, and backup status
- Notification system: controller-side notifier sends events to hub relay,
  with cooldown tracking and event-type filtering
- Notification preferences UI: email, event checkboxes, cooldown settings
  on the settings page with test email functionality
- Settings refactored: shared settingsData() helper, NotificationPrefs
  struct with getter/setter and defaults

New files:
- controller/internal/web/alerts.go (AlertManager)
- controller/internal/notify/notifier.go (hub notification client)

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

controller/internal/web/templates/monitoring.html

@@ -36,6 +36,37 @@
     </div>
 </div>
 
+<!-- Section 1.5: Remote Monitoring Status -->
+<div class="monitor-card">
+    <h3>Távoli monitoring</h3>
+    {{if not .MonitoringEnabled}}
+    <div class="monitoring-banner monitoring-banner-red">
+        ⚠️ A távoli monitoring ki van kapcsolva. Az üzemeltető nem kap értesítést hibák esetén.
+    </div>
+    {{else}}
+        {{if .AllPingsConfigured}}
+        <div class="monitoring-banner monitoring-banner-green">
+            ✅ Minden távoli monitoring aktív — az üzemeltető értesítést kap hibák esetén.
+        </div>
+        {{else}}
+        <div class="monitoring-banner monitoring-banner-yellow">
+            ⚠️ Egyes monitoring ellenőrzések nincsenek beállítva. Kérd az üzemeltetőt a konfiguráláshoz.
+        </div>
+        {{end}}
+    <div class="sysinfo-grid" style="margin-top: 0.75rem">
+        {{range .PingStatus}}
+        <div class="sysinfo-row">
+            <span class="sysinfo-label">{{.Icon}} {{.Label}}</span>
+            <span class="sysinfo-value">
+                {{if .Configured}}<span class="ping-status-ok">✅ Beállítva</span>{{else}}<span class="ping-status-warn">⚠️ Nincs beállítva</span>{{end}}
+                <span class="ping-schedule">{{.Schedule}}</span>
+            </span>
+        </div>
+        {{end}}
+    </div>
+    {{end}}
+</div>
+
 <!-- Section 2: System Metrics Charts -->
 <div class="monitor-card">
     <div class="monitor-card-header">