Chore: fix long line class paths in fxml files by using imports

Refs #122

src/main/resources/ui-structure/gameuicomponents/chatui/chatbox.fxml

@@ -3,6 +3,7 @@
 <?import javafx.geometry.*?>
 <?import javafx.scene.control.*?>
 <?import javafx.scene.layout.*?>
+<?import ch.unibas.dmi.dbis.cs108.casono.client.ui.gameuicomponents.ChatViewController?>
 
 <!--
     Dieses Fenster wird später mit den Serveranfragen verknüpft,
@@ -19,7 +20,7 @@
 
 <VBox xmlns="http://javafx.com/javafx/21"
       xmlns:fx="http://javafx.com/fxml/1"
-      fx:controller="ch.unibas.dmi.dbis.cs108.casono.client.ui.chatui.ChatViewController"
+      fx:controller="ChatViewController"
       alignment="CENTER"
       stylesheets="@chatui.css">