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/store/store.go

@@ -151,6 +151,43 @@ func (s *Store) LogNotification(customerID, eventType, severity, message, status
 	return err
 }
 
+// NotificationLogEntry represents a single notification log record.
+type NotificationLogEntry struct {
+	EventType    string
+	Severity     string
+	Message      string
+	Status       string // "sent", "skipped", "failed"
+	ErrorMessage string
+	CreatedAt    time.Time
+}
+
+// GetRecentNotifications returns the most recent notification log entries for a customer.
+func (s *Store) GetRecentNotifications(customerID string, limit int) ([]NotificationLogEntry, error) {
+	rows, err := s.db.Query(`
+		SELECT event_type, severity, message, status, COALESCE(error_message, ''), created_at
+		FROM notification_log
+		WHERE customer_id = ?
+		ORDER BY created_at DESC
+		LIMIT ?`, customerID, limit)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var entries []NotificationLogEntry
+	for rows.Next() {
+		var e NotificationLogEntry
+		var createdAt, errorMsg string
+		if err := rows.Scan(&e.EventType, &e.Severity, &e.Message, &e.Status, &errorMsg, &createdAt); err != nil {
+			return nil, err
+		}
+		e.CreatedAt = parseSQLiteTime(createdAt)
+		e.ErrorMessage = errorMsg
+		entries = append(entries, e)
+	}
+	return entries, rows.Err()
+}
+
 // SaveReport stores a new report. The reportJSON should be the raw JSON payload.
 func (s *Store) SaveReport(customerID string, reportJSON []byte) error {
 	// Parse denormalized fields from the JSON