feat(ai-research-workflows): experiment redesign — worktree isolation

[cdcore09]

Summary

Update the experiment command and template to use git worktrees for isolated experimentation, replacing the current branch/directory approach. Add worktree management guidance, cleanup verification, and fallback for non-worktree environments.

Requirements

• Replace git checkout -b and .experiments/ guidance with worktree isolation (Claude Code isolation: "worktree" or manual git worktree add)
• Add ## Worktree Management section: create, run, compare, cleanup worktrees
• Document fallback for environments without worktree support
• Update experiment template with **Worktree:** metadata field and ## Worktree Details section
• Add ## Retreat Path section to template (plan changes needed → /iterate-plan, no viable approach → back to /plan)
• Update quality checklist to include worktree cleanup verification
• Ensure experiment document captures worktree location and cleanup status

Context

Phase 2 of the workflow redesign plan. Depends on Phase 1 (orchestrator references worktree patterns).

The current experiment command suggests git checkout -b experiment-[slug] or mkdir -p .experiments/ — both pollute the working tree. Worktrees provide true isolation.

Implementation Notes

Key files:

• plugins/ai-research-workflows/commands/experiment.md (lines 147-149 for current isolation guidance)
• plugins/ai-research-workflows/skills/research-workflow-management/assets/experiment-template.md