Feature request: Allow configuring where /plan command stores plan files

Feature Request

Currently plan files are stored in ~/.claude/plans/ which is user-global. It would be useful to have a setting to store plans in the project directory (e.g., .claude/plans/) so that:

• Plans are project-specific
• Teams can optionally commit and share plans
• Plans can be gitignored for personal use

Suggested Implementation

Add a setting in .claude/settings.json:

{
  "planDirectory": ".claude/plans"
}

This would allow:

1. Default behavior unchanged - Plans still go to ~/.claude/plans/ by default
2. Per-project plans - Set planDirectory to a relative path like .claude/plans for project-local storage
3. Team collaboration - Teams could commit plans to share context
4. Privacy option - Individual developers can add the directory to .gitignore for personal use

Use Cases

• Multi-project workflows: Keep plans organized per-project instead of mixed in one global folder
• Team handoffs: Share implementation plans with teammates via version control
• Context preservation: Plans stay with the project, making it easier to resume work after switching contexts