Fix all WindowsAIFoundry according to public doc

[Gordon Lam (yeelam-gordon)]

Description

According to https://learn.microsoft.com/en-us/windows/ai/apis/get-started?tabs=winget%2Cwinui%2Cwinui2, there are multiple changes before the AI API can be used.
This pull request updates the Windows AI Foundry samples to support new system AI model capabilities and aligns the app manifest with the latest Windows versions. The most important changes are grouped below:

Manifest and capability updates:

• Added the systemAIModels capability to all relevant AppxManifest.xml and Package.appxmanifest files, enabling access to system AI models in sample applications. [1] [2] [3] [4] [5] [6] [7] [8]
• Updated TargetDeviceFamily MaxVersionTested to 10.0.26226.0 in all manifests for improved compatibility with the latest Windows releases. [1] [2] [3] [4]

WinForms sample code refactor (both packaged and sparse):

• Replaced usage of LanguageModel and text summarization with ImageDescriptionGenerator and image description functionality, including changes to model loading, error handling, and UI text. [1] [2] [3] [4] [5] [6]

Project and build improvements:

• Added a global.json specifying .NET SDK version 8.0.100 and MSBuild SDKs for Maui sample to ensure build consistency.
• Updated WinForms packaged project properties to prevent manifest version replacement for OS min/max versions.
• Added troubleshooting note to Maui sample README for resolving missing workload errors.<!--
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Target Release

1.8 and 2.0

[Copilot]

Pull Request Overview

This pull request updates the Windows AI Foundry WPF sample to enable system AI model capabilities by adding the required manifest changes and project configuration updates as specified in the Windows AI documentation.

• Added systemai namespace and systemAIModels capability to the app manifest
• Updated MaxVersionTested to 10.0.26226.0 for Windows Insider build compatibility
• Configured project to prevent automatic OS version replacement in manifest

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
WindowsAISampleForWPFSparse.csproj	Added properties to disable automatic manifest OS version replacement
AppxManifest.xml	Added systemai namespace, systemAIModels capability, and updated MaxVersionTested version

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[Copilot]

Pull Request Overview

Copilot reviewed 19 out of 19 changed files in this pull request and generated 13 comments.

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