Refactor metadata handling in PLib video library manager to improve video matching accuracy. Introduce new properties for tracking when metadata was applied and from which source. Update LibraryService and related components to utilize these properties, ensuring videos without synopses are correctly identified as matched. Enhance UI to display the library's own thumbnail alongside candidate matches, improving user decision-making. Revise README.md to reflect these changes and clarify metadata application processes.

src/PLib.Desktop/Themes/LibraryStyles.axaml

@@ -297,6 +297,19 @@
     <Setter Property="RenderTransform" Value="none" />
   </Style>
 
+  <!--
+    Says where a picture came from. Every frame on the metadata page carries one: the page
+    exists to decide whether a proposal is the same video as the file, and two unlabelled
+    frames side by side make that decision impossible to state, let alone make.
+  -->
+  <Style Selector="TextBlock.imageCaption">
+    <Setter Property="FontSize" Value="10.5" />
+    <Setter Property="FontWeight" Value="SemiBold" />
+    <Setter Property="MaxWidth" Value="128" />
+    <Setter Property="TextTrimming" Value="CharacterEllipsis" />
+    <Setter Property="Foreground" Value="{DynamicResource TextTertiaryBrush}" />
+  </Style>
+
   <Style Selector="TextBlock.taskTitle">
     <Setter Property="Foreground" Value="{DynamicResource TextPrimaryBrush}" />
     <Setter Property="FontSize" Value="12.5" />