"What's new" improvements (#44638)

<!-- 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

TO DO: Upgrade to the latest version of MarkdownTextBlock:
https://github.com/CommunityToolkit/Labs-Windows/pull/771

This PR introduces the following changes:
**Removed the custom titlebars on the OOBE Window, and replaced it with
the inbox WinUI `TitleBar` control.**

**New "What's new" experience following the VS Code release notes
experience**
- Created a new SCOOBE Windows that is a standalone window to better
visualize release notes.
- Adding a nav menu on the left to easily switch between release notes,
instead of a long page.
- Point releases are combined with the latest main release.. e.g. 0.96.1
is rendered above 0.96.0.
- The 'hero image' on main release notes will automatically be rendered
at the top of the page.
- Improved markdown styling for better readability.
- Pull requests links can now be clicked.
- Upgraded `CommunityToolkit.Labs.MarkdownTextblock` to the latest
version as it includes much needed bugfixes.

<img width="1234" height="819" alt="image"
src="https://github.com/user-attachments/assets/447b3136-306b-4f24-bc7a-c022a99e8e51"
/>

Note: the blurry image shown above will be replaced in new releases by
an image that fits the right dimensions.

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## PR Checklist

- [ ] Closes: #xxx
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **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

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

---------

Co-authored-by: Leilei Zhang <leilzh@microsoft.com>

src/settings-ui/Settings.UI/SettingsXAML/App.xaml.cs

@@ -9,7 +9,6 @@ using System.IO;
 using System.Linq;
 using System.Text.Json;
 using System.Threading.Tasks;
-
 using ManagedCommon;
 using Microsoft.PowerToys.Settings.UI.Helpers;
 using Microsoft.PowerToys.Settings.UI.Library;
@@ -227,7 +226,6 @@ namespace Microsoft.PowerToys.Settings.UI
             {
                 settingsWindow = new MainWindow();
                 settingsWindow.Activate();
-                settingsWindow.ExtendsContentIntoTitleBar = true;
                 settingsWindow.NavigateToSection(StartupPage);
 
                 // https://github.com/microsoft/microsoft-ui-xaml/issues/7595 - Activate doesn't bring window to the foreground
@@ -257,11 +255,10 @@ namespace Microsoft.PowerToys.Settings.UI
                 else if (ShowScoobe)
                 {
                     PowerToysTelemetry.Log.WriteEvent(new ScoobeStartedEvent());
-                    OobeWindow scoobeWindow = new OobeWindow(OOBE.Enums.PowerToysModules.WhatsNew);
-                    scoobeWindow.Activate();
-                    scoobeWindow.ExtendsContentIntoTitleBar = true;
+                    ScoobeWindow newScoobeWindow = new ScoobeWindow();
+                    newScoobeWindow.Activate();
                     WindowHelpers.ForceTopBorder1PixelInsetOnWindows10(WindowNative.GetWindowHandle(settingsWindow));
-                    SetOobeWindow(scoobeWindow);
+                    SetScoobeWindow(newScoobeWindow);
                 }
             }
         }
@@ -339,6 +336,7 @@ namespace Microsoft.PowerToys.Settings.UI
 
         private static MainWindow settingsWindow;
         private static OobeWindow oobeWindow;
+        private static ScoobeWindow scoobeWindow;
 
         public static void ClearSettingsWindow()
         {
@@ -365,6 +363,21 @@ namespace Microsoft.PowerToys.Settings.UI
             oobeWindow = null;
         }
 
+        public static ScoobeWindow GetScoobeWindow()
+        {
+            return scoobeWindow;
+        }
+
+        public static void SetScoobeWindow(ScoobeWindow window)
+        {
+            scoobeWindow = window;
+        }
+
+        public static void ClearScoobeWindow()
+        {
+            scoobeWindow = null;
+        }
+
         public static Type GetPage(string settingWindow)
         {
             switch (settingWindow)