Make plan file save location configurable

[jeherve]

Is your feature request related to a problem? Please describe.

Following up on #119 with more context about the use case.

The current docs/plans/ location within the project directory doesn't work well for developers who don't want to commit plan files to their repository. Plan files can be personal working documents rather than project artifacts, and can sometimes refer to plugins that are only installed on one person's Claude. I would personally prefer to keep them outside of my project's version control entirely.

In addition to that, saving all plans to a separate location would allow me to use a specific directory on my machine that contains all plans, sorted by projects, as well as past Claude discussions I saved at the end of a session. That separate location can be under version control, or can rely on a third-party cloud mechanism or app (think Obsidian or just iCloud / Google drive).

Describe the solution you'd like

Make the plan save location configurable via one of:

• A setting in the plugin configuration
• An environment variable (e.g., SUPERPOWERS_PLANS_DIR)
• A fallback hierarchy: project docs/plans/ → global ~/.claude/plans/<project-name>/

This would preserve the current default behavior while giving users flexibility.

Describe alternatives you've considered

• Adding docs/plans/ to .gitignore — solves only half of my project, and requires modifying each project's .gitignore
• Symlinking docs/plans/ to an external directory — fragile and requires manual setup per project
• Adding a learned rule to CLAUDE.md to never commit plan files — helps prevent accidental commits but doesn't solve the underlying organizational issue

Additional context

None of the workarounds feel clean. A configurable location would let users who prefer the current behavior keep it while accommodating those who want plans stored centrally or outside their repositories.

[obra]

The change I'm making for the next release of Superpowers is explicit instructions that the model should treat user preferences in Claude.md as higher priority than the skills documentation.