Hub: add preferences sync endpoint + notification display on customer page

- POST /api/v1/preferences: accepts {customer_id, email, enabled_events} from controller
- GetRecentNotifications() store method for last N notification log entries
- Customer detail page: new Notifications section (email, events, recent log table)
- joinStrings template function for event list display

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

hub/internal/web/server.go

@@ -30,7 +30,8 @@ func New(store *store.Store, passwordHash string, staleThreshold time.Duration,
 		"statusColor": statusColor,
 		"statusIcon":  statusIcon,
 		"formatFloat": func(f float64) string { return fmt.Sprintf("%.0f", f) },
-		"json":        func(v interface{}) template.JS {
+		"joinStrings": func(s []string, sep string) string { return strings.Join(s, sep) },
+		"json": func(v interface{}) template.JS {
 			b, _ := json.Marshal(v)
 			return template.JS(b)
 		},
@@ -184,11 +185,17 @@ func (s *Server) handleCustomerDetail(w http.ResponseWriter, r *http.Request, cu
 	// Get history (last 24h)
 	history, _ := s.store.GetCustomerHistory(customerID, 24*time.Hour)
 
+	// Get notification preferences and recent log
+	notifPrefs, _ := s.store.GetNotificationPrefs(customerID)
+	recentNotifs, _ := s.store.GetRecentNotifications(customerID, 10)
+
 	type detailData struct {
-		Customer *store.CustomerSummary
-		Report   map[string]interface{}
-		History  []store.CustomerSummary
-		OverallStatus string
+		Customer            *store.CustomerSummary
+		Report              map[string]interface{}
+		History             []store.CustomerSummary
+		OverallStatus       string
+		NotifPrefs          *store.NotificationPrefs
+		RecentNotifications []store.NotificationLogEntry
 	}
 
 	overallStatus := "ok"
@@ -201,10 +208,12 @@ func (s *Server) handleCustomerDetail(w http.ResponseWriter, r *http.Request, cu
 	}
 
 	data := detailData{
-		Customer: customer,
-		Report:   report,
-		History:  history,
-		OverallStatus: overallStatus,
+		Customer:            customer,
+		Report:              report,
+		History:             history,
+		OverallStatus:       overallStatus,
+		NotifPrefs:          notifPrefs,
+		RecentNotifications: recentNotifs,
 	}
 
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")