fix(brainstorming): honor CLAUDE.md Output Paths before defaults

[txhno]

Summary

• make brainstorming explicitly check CLAUDE.md Output Paths before default spec path
• make writing-plans explicitly check CLAUDE.md Output Paths before default plan path
• add README example showing Output Paths overrides and precedence

Why

Issue #939 reports that the concrete default path in skill text wins over configured output locations. This change makes override precedence explicit in both skills and user-facing docs.

Closes #939

[obra]

This looks pretty hacky and completely ignores the pull request template which strongly suggests that this wasn't tested.

[txhno]

You're right. This was a bad PR shape.

I bundled behavior-shaping skill edits with the README change, ignored the PR template, and I did not have adversarial eval results in hand before opening it. I tried to run the repo's local Claude-based test harness now, but claude is not installed on this machine, so I can't honestly retroactively claim proper eval coverage.

I also should have credited the original work more clearly: the workaround and concrete reproduction on #939 came from @shalinhudda, and @obra had already suggested that the right direction was a README example rather than the broader skill-text changes I submitted.

Sorry for wasting your review time.