feat: Validate recurrence date before updating RecursNext

sync/service/postgres.go

@@ -150,6 +150,11 @@ func (p *Postgres) RecursNext(id string, date time.Time) error {
 		return ErrNotARecurrer
 	}
 
+	// Verify that the new date is actually a valid recurrence
+	if !recurrer.On(date) {
+		return fmt.Errorf("%w: date %v is not a valid recurrence", ErrPostgresFailure, date)
+	}
+
 	_, err = p.db.Exec(`
 		UPDATE items 
 		SET recur_next = $1