Add packaged source fallback for noninteractive runs

[PrzemyslawKlys]

📖 Description

Fixes packaged source initialization for noninteractive runs where the MSIX source package cannot be deployed for the current user session.

In this case, opening the packaged source can fail before the source index is available, which leaves commands such as winget list unable to query the default winget source.

This change adds a local fallback copy of the packaged source index. When packaged deployment is blocked in a noninteractive context, winget can open the fallback source data instead of failing the source open completely.

The fallback is kept in sync after successful packaged source updates and is only preferred when it is newer or when the packaged source cannot be opened. Invalid or unusable fallback data is treated as missing so future source updates can repair it.

🔗 References

Fixes #6334.

🔍 Validation

Validated with focused repository-core build coverage and a live noninteractive Windows Server 2025 remoting scenario:

• current shipping winget reproduced the packaged source deployment failure and returned no winget source results
• the updated development build completed winget list successfully using the winget source
• logs showed the packaged deployment failure followed by the local fallback source path being used

Also validated focused source fallback behavior around:

• missing fallback data
• corrupt fallback version metadata
• successful packaged source updates refreshing fallback data
• newer fallback selection
• fallback invalidation when a newer fallback cannot be opened

✅ Checklist

• Signed the Contributor License Agreement
• Linked to an issue
• Updated Release Notes (if applicable)
• Updated documentation (if applicable)
• Updated Copilot instructions (if build, architecture, or conventions changed)

📋 Issue Type

• Bug fix
• Feature
• Task

Microsoft Reviewers: Open in CodeFlow