UI-Verbesserungen: Splitter-Verhalten und Layout optimiert

Verbesserungen am Haupt-Layout:
- Splitter: opaqueResize deaktiviert für flüssigeres Resizing
- Splitter: childrenCollapsible deaktiviert (verhindert versehentliches Kollabieren)
- TreeWidget: Hover-Effekt auskommentiert (weniger visuelles Rauschen)
- Frame-Eigenschaften angepasst für konsistentes Styling
- Placeholder-Labels (label_3, label_4) aus UI entfernt

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/ui/MainWinddow.ui

@@ -32,6 +32,12 @@
       <property name="orientation">
        <enum>Qt::Orientation::Horizontal</enum>
       </property>
+      <property name="opaqueResize">
+       <bool>false</bool>
+      </property>
+      <property name="childrenCollapsible">
+       <bool>false</bool>
+      </property>
       <widget class="QFrame" name="frame">
        <property name="sizePolicy">
         <sizepolicy hsizetype="Preferred" vsizetype="Preferred">
@@ -168,6 +174,12 @@
          <verstretch>0</verstretch>
         </sizepolicy>
        </property>
+       <property name="frameShadow">
+        <enum>QFrame::Shadow::Raised</enum>
+       </property>
+       <property name="midLineWidth">
+        <number>1</number>
+       </property>
        <property name="widgetResizable">
         <bool>true</bool>
        </property>
@@ -213,7 +225,7 @@
       </widget>
       <widget class="QFrame" name="frame_3">
        <property name="frameShape">
-        <enum>QFrame::Shape::NoFrame</enum>
+        <enum>QFrame::Shape::StyledPanel</enum>
        </property>
        <property name="frameShadow">
         <enum>QFrame::Shadow::Raised</enum>
@@ -234,7 +246,7 @@
         <item>
          <widget class="QFrame" name="frame_4">
           <property name="frameShape">
-           <enum>QFrame::Shape::StyledPanel</enum>
+           <enum>QFrame::Shape::NoFrame</enum>
           </property>
           <property name="frameShadow">
            <enum>QFrame::Shadow::Raised</enum>
@@ -369,6 +381,12 @@
         </item>
         <item>
          <widget class="QScrollArea" name="scrollArea_2">
+          <property name="frameShape">
+           <enum>QFrame::Shape::NoFrame</enum>
+          </property>
+          <property name="frameShadow">
+           <enum>QFrame::Shadow::Raised</enum>
+          </property>
           <property name="widgetResizable">
            <bool>true</bool>
           </property>
@@ -378,7 +396,7 @@
              <x>0</x>
              <y>0</y>
              <width>726</width>
-             <height>695</height>
+             <height>697</height>
             </rect>
            </property>
            <layout class="QVBoxLayout" name="verticalLayout_3">
@@ -394,20 +412,6 @@
             <property name="bottomMargin">
              <number>0</number>
             </property>
-            <item>
-             <widget class="QLabel" name="label_3">
-              <property name="text">
-               <string>TextLabel</string>
-              </property>
-             </widget>
-            </item>
-            <item>
-             <widget class="QLabel" name="label_4">
-              <property name="text">
-               <string>TextLabel</string>
-              </property>
-             </widget>
-            </item>
            </layout>
           </widget>
          </widget>
@@ -432,7 +436,6 @@
      <string>Projekt</string>
     </property>
     <addaction name="actionNeu"/>
-    <addaction name="action_ffnen"/>
     <addaction name="separator"/>
     <addaction name="actionVorhandene_Projekte"/>
     <addaction name="separator"/>
@@ -460,17 +463,6 @@
     <string>Ctrl+N</string>
    </property>
   </action>
-  <action name="action_ffnen">
-   <property name="icon">
-    <iconset theme="folder-open"/>
-   </property>
-   <property name="text">
-    <string>Öffnen ...</string>
-   </property>
-   <property name="shortcut">
-    <string>Ctrl+O</string>
-   </property>
-  </action>
   <action name="actionBeenden">
    <property name="icon">
     <iconset theme="QIcon::ThemeIcon::ApplicationExit"/>