Close setup path escape and verify packed upgrades

[liolevx]

Summary

• Refuse linked setup destinations before initialization writes, including changes introduced after preview.
• Guard application and rollback paths; preserve unrelated links and user-owned content.
• Rehearse real packed CLI installation, repeated init, managed-pin sync, and refusal behavior.
• Retain the independent review and release acceptance report.

Validation

• Full Windows check: 184 tests passed.
• Full Linux check: 182 passed, two Windows-only tests skipped.
• Real tarball installation and upgrade rehearsal passed on both platforms.
• Independent reviewer approved the safety fix.
• Local advisory audit timed out; the GitHub package job reruns it.

Remaining release gate

A real signed-in coding-agent workflow remains pending. No npm publication is part of this PR.

Three focused commits are preserved.