fix: move Styles.xaml to Application.Resources so dark ToolTip applies

WPF ToolTip popups open in their own top-level window and only inherit
from Application.Resources, not from Window-scoped resource dictionaries.
Moving the merge to App.xaml makes the dark ToolTip style apply globally.

Author: GokulMV

src/ClipHive/App.xaml

@@ -2,5 +2,10 @@
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
     <Application.Resources>
+        <ResourceDictionary>
+            <ResourceDictionary.MergedDictionaries>
+                <ResourceDictionary Source="/ClipHive;component/Resources/Styles.xaml" />
+            </ResourceDictionary.MergedDictionaries>
+        </ResourceDictionary>
     </Application.Resources>
 </Application>

src/ClipHive/Views/SidebarWindow.xaml

@@ -18,15 +18,7 @@
         Deactivated="Window_Deactivated"
         PreviewKeyDown="Window_KeyDown">
 
-    <Window.Resources>
-        <ResourceDictionary>
-            <ResourceDictionary.MergedDictionaries>
-                <ResourceDictionary Source="/ClipHive;component/Resources/Styles.xaml" />
-            </ResourceDictionary.MergedDictionaries>
-        </ResourceDictionary>
-    </Window.Resources>
-
-    <Border x:Name="RootBorder"
+<Border x:Name="RootBorder"
             CornerRadius="8"
             Background="#CC1A1A1A"
             BorderBrush="#3A3A3A"