Prettier 3 (pinned), printWidth 100, double quotes — chosen to match the existing hand-formatting and minimise reflow. This commit is ONLY the mechanical format pass (`prettier --write`) plus the config/ignore/scripts, isolated so it never pollutes a feature diff. Verified behaviour-neutral: typecheck, eslint (0 errors), and vitest all green before and after. See .git-blame-ignore-revs — `git blame` skips this sha.