Search UX improvements (#41386)

### Fixing visual glitch in the 'Show all results' template:

Before
<img width="588" height="103" alt="image"
src="https://github.com/user-attachments/assets/00da60ea-d0ab-4ffe-8f69-75be7e537d63"
/>

After
<img width="598" height="70" alt="image"
src="https://github.com/user-attachments/assets/dc859731-8783-494a-b561-ea6396ca69b3"
/>


### Displaying "Show results for * search term *" on search results page
Before
<img width="716" height="239" alt="image"
src="https://github.com/user-attachments/assets/a80e6e58-df88-47b2-85ab-c39cbdc88690"
/>

After
<img width="349" height="264" alt="image"
src="https://github.com/user-attachments/assets/99029ee6-94f7-4454-a443-640c22f9e6f3"
/>


### Using Accent Color for the search highlight for better visibility
and fixing a bug
Before

![highlight-bug](https://github.com/user-attachments/assets/2d4c0f5b-4030-4c10-a4ec-c7c5023034f0)


After


![fix-accent](https://github.com/user-attachments/assets/62a223a9-9360-4297-9127-5aaef82c162f)

---------

Co-authored-by: vanzue <vanzue@outlook.com>

src/settings-ui/Settings.UI/SettingsXAML/Views/ShellPage.xaml

@@ -57,12 +57,6 @@
         </DataTemplate>
         <DataTemplate x:Key="NoResultSearchResultTemplate" x:DataType="models:SuggestionItem">
             <Grid>
-                <Rectangle
-                    Height="1"
-                    Margin="0,-4,0,0"
-                    HorizontalAlignment="Stretch"
-                    VerticalAlignment="Top"
-                    Fill="{ThemeResource DividerStrokeColorDefaultBrush}" />
                 <TextBlock
                     Margin="8"
                     HorizontalAlignment="Center"
@@ -71,10 +65,10 @@
             </Grid>
         </DataTemplate>
         <DataTemplate x:Key="ShowAllSearchResultTemplate" x:DataType="models:SuggestionItem">
-            <Grid Padding="16,8">
+            <Grid>
                 <Rectangle
                     Height="1"
-                    Margin="0,-4,0,0"
+                    Margin="0,-12,0,0"
                     HorizontalAlignment="Stretch"
                     VerticalAlignment="Top"
                     Fill="{ThemeResource DividerStrokeColorDefaultBrush}" />
@@ -92,7 +86,6 @@
             <ic:InvokeCommandAction Command="{x:Bind ViewModel.LoadedCommand}" />
         </ic:EventTriggerBehavior>
     </i:Interaction.Behaviors>
-
     <Grid x:Name="RootGrid">
         <Grid.RowDefinitions>
             <RowDefinition Height="48" />