Add PR review notes; hardlink detection and changelog stdio fixes

[cenglin123]

Motivation

• Prevent incorrect detection of hardlink groups on filesystems where inode values are unreliable by requiring link-count signal.
• Avoid stdout/stderr encoding crashes on Windows by forcing UTF-8-compatible stdio when possible.
• Provide an on-repo PR_REVIEW.md note to clarify commit/merge process and recommended checks.

Description

• Add PR_REVIEW.md with guidance about the PR status, maintainer clarification, and recommended CI checks.
• Update assets/scripts/agent_links.py to make is_hardlink_group() return false unless all link keys are present and each file has st_nlink > 1, and to handle OSError when reading stat.
• Update assets/scripts/changelog.py by adding configure_stdio() and emit() helpers, replacing direct print() calls with emit() to safely write UTF-8 output, and calling configure_stdio() from main().

Testing

• No automated tests were executed as part of this rollout; please run the repository test suite with pytest and any CI pre-commit hooks before merging.

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Codex Task