docs(package-json): clarify repository field normalization

[MaxBlack-dev]

Description

This PR documents npm's normalization behavior for the repository field in package.json during publishing.

Changes

• Added a "Note on normalization" section explaining that npm converts shorthand repository formats to the full object format during npm publish
• Documented the warning message users see when publishing with shorthand formats
• Recommended using the full object format to avoid warnings
• Mentioned npm pkg fix as a tool to automatically convert to normalized format

Context

Users were confused when npm publish showed warnings about auto-correcting the repository field, even though the documentation stated shorthand formats were allowed. The maintainer (@wraithgar) explained that npm has historically normalized this field during publishing, creating a discrepancy between local package.json and the published manifest. The warning is preparing users for future changes where this discrepancy may no longer be allowed.

Closes #7299