Add developer account guidance and cross-references for Windows App SDK

[Copilot]

This change addresses the difficulty developers face when trying to access free developer registration for Windows App SDK, as reported by a developer from India.

Problem

The Windows App SDK documentation lacked clear guidance on developer account requirements and didn't connect users to the available free registration process. Developers learning about Windows App SDK had no clear path to understand they needed a developer account for publishing, or that free registration was available in their region.

Solution

Added targeted improvements to bridge the gap between Windows App SDK documentation and developer account registration:

In hub/apps/windows-app-sdk/index.md:

• Added a new "Developer account for publishing apps" section with clear guidance
• Highlighted that individual developers can register for free in select markets including India
• Provided step-by-step instructions linking to storedeveloper.microsoft.com
• Included direct support contact information (storesupport@service.microsoft.com)
• Added cross-reference to free developer registration documentation

In hub/apps/publish/whats-new-individual-developer.md:

• Added a tip section specifically for Windows App SDK developers
• Created bidirectional cross-reference to improve discoverability

Impact

These minimal changes ensure developers like Tabrez Ahmed from Bangalore can:

• Easily discover free registration is available in India
• Follow a clear path from Windows App SDK docs to developer account setup
• Access support when needed during the registration process
• Understand the connection between SDK development and Store publishing

The changes maintain the existing documentation structure while filling critical gaps in the developer onboarding experience.

Fixes #5592.

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[learn-build-service-prod]

Learn Build status updates of commit 27dfd36:

⚠️ Validation status: warnings

For more details, please refer to the build report.

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[learn-build-service-prod]

Learn Build status updates of commit 5d9fae0:

✅ Validation status: passed

File	Status	Preview URL	Details
hub/apps/publish/whats-new-individual-developer.md	✅Succeeded
hub/apps/windows-app-sdk/index.md	✅Succeeded

For more details, please refer to the build report.

[prmerger-automator]

PRMerger Results

Issue	Description
File Change Percent	This PR contains file(s) with more than 30% file change.
Index File	This PR contains a change to the index file.

[learn-build-service-prod]

Learn Build status updates of commit 5d9fae0:

✅ Validation status: passed

File	Status	Preview URL	Details
hub/apps/publish/whats-new-individual-developer.md	✅Succeeded
hub/apps/windows-app-sdk/index.md	✅Succeeded

For more details, please refer to the build report.

[prmerger-automator]

PRMerger Results

Issue	Description
File Change Percent	This PR contains file(s) with more than 30% file change.
Index File	This PR contains a change to the index file.