fix: bootstrap stable plugin data root

[vitry]

Summary

• derive a stable marketplace-qualified plugin data root when skill commands lack PLUGIN_DATA
• bootstrap the root through Codex user/profile writable-root configuration before persisting plugin state
• unify skill and hook resolution, including symlink and Windows-safe path handling

Test plan

• npm run check
• installed marketplace setup without PLUGIN_DATA/PLUGIN_ROOT
• restart/rerun setup reaches ready state
• subagent spec review approved
• subagent code-quality review approved