Refine UI layout in PLib video library manager by adjusting MainWindow and SettingsView for a more cohesive design. Implement dedicated styles for panel headers and footers, ensuring consistent visual hierarchy. Update README.md to document these layout enhancements and style changes.

src/PLib.Desktop/Themes/LibraryStyles.axaml

@@ -127,6 +127,30 @@
     <Setter Property="BorderThickness" Value="0,1,0,0" />
   </Style>
 
+  <!--
+    The panel's own header and action row. Deliberately lighter than the window bars above:
+    they belong to a region inside the content, and giving them the same weight made the two
+    halves read as two applications stitched together.
+  -->
+  <Style Selector="Border.panelHeader">
+    <Setter Property="Padding" Value="16,13" />
+    <Setter Property="BorderBrush" Value="{DynamicResource SurfaceBorderBrush}" />
+    <Setter Property="BorderThickness" Value="0,0,0,1" />
+  </Style>
+
+  <Style Selector="Border.panelFooter">
+    <Setter Property="Padding" Value="16,12" />
+    <Setter Property="BorderBrush" Value="{DynamicResource SurfaceBorderBrush}" />
+    <Setter Property="BorderThickness" Value="0,1,0,0" />
+  </Style>
+
+  <Style Selector="TextBlock.panelTitle">
+    <Setter Property="Foreground" Value="{DynamicResource TextPrimaryBrush}" />
+    <Setter Property="FontSize" Value="14" />
+    <Setter Property="FontWeight" Value="SemiBold" />
+    <Setter Property="VerticalAlignment" Value="Center" />
+  </Style>
+
   <!-- ======================== Settings panel ======================== -->
 
   <!--
@@ -138,14 +162,11 @@
   <Style Selector="Border.settingsPanel">
     <Setter Property="Width" Value="0" />
     <Setter Property="ClipToBounds" Value="True" />
-    <!--
-      Its own backdrop and a stronger divider than the usual surface border: once the bars on
-      both sides line up, a hairline in the ordinary border colour reads as one continuous
-      bar and the panel stops looking like a separate region.
-    -->
+    <!-- Its own backdrop, so the panel reads as a separate region even where the bars on
+         both sides share a colour. The divider itself is a sibling element, not this
+         border: a border belongs to the panel and is only as visible as the panel's own
+         background, whereas the separation has to hold across the bars too. -->
     <Setter Property="Background" Value="{DynamicResource PanelBackgroundBrush}" />
-    <Setter Property="BorderBrush" Value="{DynamicResource PanelDividerBrush}" />
-    <Setter Property="BorderThickness" Value="1,0,0,0" />
     <Setter Property="Transitions">
       <Transitions>
         <DoubleTransition Property="Width" Duration="0:0:0.22" Easing="CubicEaseOut" />
@@ -157,6 +178,16 @@
     <Setter Property="Width" Value="400" />
   </Style>
 
+  <!--
+    Drawn after the panel and over both bars, so nothing can paint across it. This is the
+    one line that tells the eye where the library ends and the settings begin.
+  -->
+  <Style Selector="Rectangle.panelDivider">
+    <Setter Property="Width" Value="1" />
+    <Setter Property="HorizontalAlignment" Value="Left" />
+    <Setter Property="Fill" Value="{DynamicResource PanelDividerBrush}" />
+  </Style>
+
   <!-- ============================ Badge ============================ -->
 
   <Style Selector="Border.badge">