Enable/disable relies on symlinks — breaks on Windows

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Problem

devloop rules enable/disable uses symlinks (ln -sfn) to manage active packs in ~/devloop/rules/. On Windows, symlinks require Developer Mode or admin privileges, so this fails for most users.

Options

1. Directory junctions (mklink /J) — work without admin on Windows but only for directories. Needs OS detection.
2. Copy instead of symlink — portable but changes don't propagate and update becomes more complex.
3. Config file listing enabled packs — a plain text file (like the old rule-layers approach) that resolve-rules reads. No filesystem tricks needed. Most portable.

Notes

• resolve-rules scans ~/devloop/rules/ and follows symlinks to find .md files. Any fix needs to keep that contract or update resolve-rules in the devloop plugin to match.
• Project-level rules ({cwd}/devloop/rules/) are unaffected — they're regular files.
• The README already has a Windows prerequisite note but it only covers bash/jq, not the symlink requirement.