Resolve conflicts after 914 upstream commits:
- CHANGELOG.md: keep brew opencode fix entry in Unreleased
- .gitignore: keep superpowers docs exclusion, take upstream additions
Drop /usr/local/ TOOLCHAIN_SEGMENTS addition — /usr/local/bin is part
of the default macOS PATH, so treating it as user-configured would skip
the login-shell fallback that this fix relies on. Upstream tests
(pass 1602) confirm minimal system PATH must not look user-configured.
Mayuresh Kadu
d671119884