#19 UX: -h should surface the skill instead of duplicating contract text

Idea: per-verb -h strings are hand-maintained and generic (agents end up reading spec/schema.md anyway); every extra help string is duplicated contract that can drift. Make f0rge <cmd> -h = one usage line + pointer to the contract (f0rge --skill), so the skill is the single source of truth. Budgets keep applying: -h <=250B/8 lines, root <=300B/12, skill <=900B/30 — pick the compact shape that fits (e.g. usage line + "contract: f0rge --skill"). No core changes; docs/UX only (cmd/*.rs help() strings, skill.rs). Acceptance: budget tests green; no -h string paraphrases contract prose that --skill already owns.