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This PR follows up on #20418 by implementing the automatic mitigation requested in the source code comment. It changes the pkgconf macOS SDK mismatch diagnostic from a passive warning to adds an active repair attempt.

The diagnostic check update-report and upgrade now perform the following steps:

1. Detects if pkgconf was built on a different version of macOS.
2. If a mismatch is found, it informs the user and automatically attempts to run brew reinstall pkgconf.
3. If the automatic reinstall fails, it reports the error and provides the manual command as a fallback.

This provides a better user experience by solving the issue directly for the underlying problem noted in issue #16137.