samples: sync NotesApp with latest ACI API changes

[surajkumar-08]

Summary

Update NotesApp sample to WinAppSDK 2.0.0-preview1 ACI API surface

Namespace & API renames

• Update namespace from Microsoft.Windows.AI.Search.Experimental.AppContentIndex to Microsoft.Windows.Search.AppContentIndex
• Rename Remove → RemoveContentItem, RemoveAll → RemoveAllContentItems
• Use RegionOfInterest (on AppManagedImageQueryMatch) instead of Subregion (which remains on AppManagedOcrTextQueryMatch for OCR matches)

New API usage

• Add pre-flight system capability checks via GetIndexCapabilitiesOfCurrentSystem() before creating an index
• Subscribe to AppContentIndexListener events (IndexCapabilitiesChanged, IndexStatisticsChanged, ContentItemStatusChanged) for live index monitoring
• Drive search UI progress bar from IndexStatisticsChanged events
• Log index statistics via GetIndexStatistics() on startup

Resource management & robustness

• Dispose AppContentIndexer in MainWindow.Closed handler
• Add IDisposable to SearchViewModel; call Dispose() via SearchView.Unloaded to release CancellationTokenSource
• Replace int.Parse with int.TryParse for image match ContentId to avoid FormatException
• Replace throw new Exception with throw new InvalidOperationException

Cleanup

• Update WinAppSDK from 2.0.0-experimental3 to 2.0.0-preview1
• Remove stale commented-out internal project references from csproj
• Fix README: correct solution filename, update SDK version reference
• Clean up Package.appxmanifest identity for public sample

Checklist

Note that /azp run currently isn't working for this repo.

• Samples build and run using the Visual Studio versions listed in the Windows development docs.
• Samples build and run on all supported platforms (x64, x86, ARM64) and configurations (Debug, Release).
• Samples set the minimum supported OS version to Windows 10 version 1809.
• Samples build clean with no warnings or errors.
• [For new samples]: Samples have completed the sample guidelines checklist and follow standardization/naming guidelines.
• Microsoft employees only: you can validate your changes by following the instructions here: https://www.osgwiki.com/wiki/WindowsAppSDK-Samples

[surajkumar-08]

@abhmondal_microsoft can you please provide your review.

[surajkumar-08]

@microsoft-github-policy-service agree company="Microsoft"