fix: properly filter by date range, improve filter handlers

templates/administrative/assignment/timeline.html.twig

@@ -104,6 +104,10 @@
                         {% endfor %}
                     </tr>
                 {% endfor %}
+            {% else %}
+                <td colspan="{{ filterDto.period | length }}">
+                    Keine Ergebnisse
+                </td>
             {% endfor %}
         </table>
     </div>