feat: Post-compact plan file re-attachment

[minpeter]

Context

Claude Code re-attaches active plan files after compaction. Our PostCompactRestorer supports file/skill restoration but not plan files.

Blocked by

Plan system doesn't exist yet in CEA/harness. Need a plan file tracking mechanism first.

When to implement

After plan system is built, add plan files to PostCompactRestorer tracking with appropriate priority (higher than regular files, lower than skills).

Reference

Claude Code: src/services/compact/postCompactCleanup.ts — re-attaches plan files from .claude/plans/ directory.