v0.3.0 — mindstorming

The brainstorming skill is now mindstorming, ending the name collision with superpowers:brainstorming and Anthropic's own brainstorming features. Trigger scoping now cedes code work to superpowers and claims non-code deliverables. Output paths move to flat docs/mindpowers/specs/ (legacy docs/brainstorm/ still read), drafts get a home, Cowork no-filesystem fallback, confidentiality warning, complete plugin metadata. See CHANGELOG for details.