CmdPal: Fix EmptyContent not rendering (#41788)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request
While testing the recent GridPages changes #40832 , I noticed that the
`EmptyContent` case was removed from the `SwitchPresenter`, which caused
EmptyContent to stop rendering.

This PR restores the missing case so that `EmptyContent` is correctly
displayed again.

### Before
<img width="790" height="480" alt="BeforeFix"
src="https://github.com/user-attachments/assets/71e43da9-41c4-4c1a-bbb1-bc3f6b4da1d0"
/>

### After
<img width="793" height="483" alt="AfterFix"
src="https://github.com/user-attachments/assets/ebec6b44-ebfd-4497-9e69-99b00ce44117"
/>


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## PR Checklist

- [ ] Closes: #41786 
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/Microsoft.CmdPal.UI/ExtViews/ListPage.xaml

@@ -306,6 +306,36 @@
                     </controls:Case>
                 </controls:SwitchPresenter>
             </controls:Case>
+            <controls:Case Value="True">
+                <StackPanel
+                    Margin="24"
+                    HorizontalAlignment="Center"
+                    VerticalAlignment="Center"
+                    Orientation="Vertical"
+                    Spacing="4">
+                    <cpcontrols:IconBox
+                        x:Name="IconBorder"
+                        Width="48"
+                        Height="48"
+                        Margin="8"
+                        Foreground="{ThemeResource TextFillColorSecondaryBrush}"
+                        SourceKey="{x:Bind ViewModel.EmptyContent.Icon, Mode=OneWay}"
+                        SourceRequested="{x:Bind help:IconCacheProvider.SourceRequested}" />
+                    <TextBlock
+                        Margin="0,4,0,0"
+                        HorizontalAlignment="Center"
+                        FontWeight="SemiBold"
+                        Text="{x:Bind ViewModel.EmptyContent.Title, Mode=OneWay}"
+                        TextAlignment="Center"
+                        TextWrapping="Wrap" />
+                    <TextBlock
+                        HorizontalAlignment="Center"
+                        Foreground="{ThemeResource TextFillColorSecondaryBrush}"
+                        Text="{x:Bind ViewModel.EmptyContent.Subtitle, Mode=OneWay}"
+                        TextAlignment="Center"
+                        TextWrapping="Wrap" />
+                </StackPanel>
+            </controls:Case>
         </controls:SwitchPresenter>
     </Grid>
 </Page>