Fix typos, broken links, and formatting issues across docs for apps

[qiutongMS]

This PR addresses various documentation issues found across multiple pages.

Typo fixes

• Fix "Window App SDK" → "Windows App SDK" in desktop landing page
• Fix duplicate "for the for the" → "for the" in WinUI Notes tutorial
• Fix "let's" → "lets" (grammatical error) in view-model tutorial
• Fix "imput" → "input" in WinUI 1.8 release notes
• Fix "indows" → "Windows" in WinUI 1.8 release notes (Object Erase section)
• Fix "AppCOntentIndexListener" → "AppContentIndexListener" in WinUI 2.0 release notes

Broken/outdated link fixes

• Update "OneDevMinute on YouTube" → "OneDevMinute on Microsoft Learn" (content moved)
• Update SparsePackages sample link → PackageWithExternalLocation (repo renamed)
• Remove broken link to retired Microsoft Accessibility Approach Datasheet
• Update archived release notes links from release-notes-archive/ to consolidated ./release-notes/ paths in downloads-archive.md
• Update CollectionsInterop sample link to new WinUI-Gallery repo location
• Fix WinUI Gallery GitHub branch reference from main to winappsdk/1.1 in 1.1 release notes
• Fix truncated ISO download link (linkid=233566 → linkid=2335668) in Windows SDK downloads
• Remove dead GitHub issue link 4646 in 1.6 release notes

Formatting/content fixes

• Fix incorrect file name "MainPage.xaml" → "MainWindow.xaml" in project setup tutorial
• Fix code fence language from csharp to xaml for XAML snippet in view-model tutorial
• Fix malformed NOTE block (missing > prefix) in WinApp SDK 0.8 release notes
• Fix unclosed → XML tag in code samples (0.8, 1.6 release notes)
• Remove extra tag in 1.6 release notes
• Fix duplicate # in issue link (#[#10374] → [#10374]) in 1.8 release notes

[learn-build-service-prod]

Learn Build status updates of commit 0c6f4a8:

✅ Validation status: passed

File	Status	Preview URL	Details
hub/apps/desktop/index.yml	✅Succeeded
hub/apps/get-started/best-practices.md	✅Succeeded
hub/apps/tutorials/winui-notes/note.md	✅Succeeded
hub/apps/tutorials/winui-notes/project.md	✅Succeeded
hub/apps/tutorials/winui-notes/view-model.md	✅Succeeded
hub/apps/windows-app-sdk/downloads-archive.md	✅Succeeded
hub/apps/windows-app-sdk/release-notes/project-reunion-0-5-preview.md	✅Succeeded
hub/apps/windows-app-sdk/release-notes/windows-app-sdk-0-8.md	✅Succeeded
hub/apps/windows-app-sdk/release-notes/windows-app-sdk-1-1.md	✅Succeeded
hub/apps/windows-app-sdk/release-notes/windows-app-sdk-1-6.md	✅Succeeded
hub/apps/windows-app-sdk/release-notes/windows-app-sdk-1-8.md	✅Succeeded
hub/apps/windows-app-sdk/release-notes/windows-app-sdk-2-0.md	✅Succeeded
hub/apps/windows-sdk/downloads.md	✅Succeeded

For more details, please refer to the build report.

[prmerger-automator]

PRMerger Results

Issue	Description
Yaml File(s)	This PR includes changes to .yml file(s) owned by another author.
Changed Files	This PR contains more than 10 changed files.