Add a third dev-cycle entry path: a specify skill that produces an
approved spec from given sources (settled in-context discussion or an
exhaustive issue) with review but no interview. Splits brainstorm's
deciding half from its producing half — brainstorm becomes optional
discovery, specify becomes the sole production gate before planner,
mirroring the RED->GREEN split that keeps tdd/debug honest. specify
bounces to brainstorm on an unresolved design fork, the same
discipline tdd uses.
