docs(config): clarify unreadable project scope fallback

[ydflow]

Summary

• Clarify that read-only commands do not migrate project data.
• Explain that the legacy double-read fallback still handles valid old configs, while an existing unreadable project config stops scope resolution instead of falling back to another project or user scope.

This follows the non-blocking documentation finding on #899, which has already merged.

Verification

• git diff --check — passed.
• Reviewed the one-file documentation diff against autoDetectInit on current main. No runtime files changed.

[github-actions]

No findings.

The PR is documentation-only, and the verification record is sufficient. Per the repository’s review rules, no real-CLI/end-to-end test is required.