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/style.css

@@ -527,6 +527,29 @@ h3 {
 }
 .form-group-auto label { margin: 0; }
 .auto-generated-badge { color: var(--green); font-size: .8rem; font-weight: 500; }
+.checkbox-group {
+    display: flex;
+    flex-direction: column;
+    gap: .5rem;
+    margin-top: .25rem;
+}
+.form-inline {
+    display: flex;
+    align-items: center;
+    gap: .75rem;
+}
+.form-control-narrow {
+    width: 80px;
+}
+.form-hint {
+    font-size: .85rem;
+    color: var(--text-muted);
+}
+.form-actions {
+    display: flex;
+    gap: .75rem;
+    margin-top: 1rem;
+}
 .form-control {
     width: 100%;
     padding: .55rem .75rem;
@@ -640,6 +663,37 @@ select.form-control option { background: var(--bg-secondary); color: var(--text-
     border-color: rgba(210, 153, 34, 0.3);
 }
 
+/* Dashboard alert banners */
+.alerts-container { margin-bottom: 1rem; }
+.alert-banner {
+    display: flex;
+    align-items: center;
+    gap: 0.75rem;
+    padding: 0.75rem 1rem;
+    border-radius: 8px;
+    margin-bottom: 0.5rem;
+    font-size: 0.9rem;
+    border: 1px solid;
+}
+.alert-banner-error {
+    background: rgba(248, 113, 113, 0.1);
+    border-color: rgba(248, 113, 113, 0.3);
+    color: #f87171;
+}
+.alert-banner-warning {
+    background: rgba(250, 204, 21, 0.1);
+    border-color: rgba(250, 204, 21, 0.3);
+    color: #facc15;
+}
+.alert-banner-info {
+    background: rgba(96, 165, 250, 0.1);
+    border-color: rgba(96, 165, 250, 0.3);
+    color: #60a5fa;
+}
+.alert-icon { flex-shrink: 0; }
+.alert-message { flex: 1; }
+.alert-link { margin-left: auto; white-space: nowrap; }
+
 /* Memory summary on deploy page */
 .memory-summary {
     background: var(--bg-card);
@@ -1488,6 +1542,34 @@ a.stat-card:hover {
 .monitor-card h3 {
     margin-bottom: .75rem;
 }
+.monitoring-banner {
+    padding: .75rem 1rem;
+    border-radius: 8px;
+    font-size: .9rem;
+    border: 1px solid;
+}
+.monitoring-banner-green {
+    background: var(--green-bg);
+    color: var(--green);
+    border-color: rgba(35, 134, 54, 0.3);
+}
+.monitoring-banner-yellow {
+    background: var(--yellow-bg);
+    color: var(--yellow);
+    border-color: rgba(210, 153, 34, 0.3);
+}
+.monitoring-banner-red {
+    background: var(--orange-bg);
+    color: var(--orange);
+    border-color: rgba(219, 109, 40, 0.3);
+}
+.ping-status-ok { color: var(--green); }
+.ping-status-warn { color: var(--yellow); }
+.ping-schedule {
+    color: var(--text-muted);
+    font-size: .85rem;
+    margin-left: .75rem;
+}
 .monitor-card-header {
     display: flex;
     align-items: center;