Controller v0.7.2: notification preferences sync to hub

- SyncPreferences() method on Notifier: POST to hub /api/v1/preferences
- IsEnabled() getter for hub connectivity check
- settingsNotificationsHandler: sync to hub after local save (3 flash message variants)
- Startup sync: non-blocking goroutine pushes prefs to hub on boot (DB rebuild recovery)
- Updated CONTEXT.md, README.md with v0.7.2 changes

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

controller/cmd/controller/main.go

@@ -237,6 +237,18 @@ func main() {
 		}()
 	}
 
+	// Sync notification preferences to hub on startup (handles hub DB rebuild recovery)
+	if notifier.IsEnabled() {
+		go func() {
+			prefs := sett.GetNotificationPrefs()
+			if prefs.Email != "" {
+				if err := notifier.SyncPreferences(prefs.Email, prefs.EnabledEvents); err != nil {
+					logger.Printf("[WARN] Failed to sync notification preferences on startup: %v", err)
+				}
+			}
+		}()
+	}
+
 	// Initial alert refresh (so alerts appear immediately, not after first 5min health check)
 	go func() {
 		report := monitor.RunHealthCheck(cfg, cpuCollector)