Dev tweaker (design exploration)

www/src/dev/tweaker is a floating panel for exploring designs/layouts live: you add useTweak() calls to a feature component, the user flips the options in the panel and picks one. It runs in dev and on Vercel previews, and is dead-code-eliminated from production builds. Full API + workflow: www/src/dev/tweaker/README.md.

• When (strict): only during active PR/feature-branch work, and only when the user explicitly asks for tweaks/options on a specific feature. Never unprompted, never on main, never as a way to add real config.
• How: add useTweak('Label', { type, default, group? }) in the relevant www feature component and branch the JSX/styles on the returned value. Keep each default equal to the current look (nothing changes until a control moves); offer a small set (≤~5) of meaningful named variants per axis; group related controls. Types: select, boolean, number, color, text.
• Boundaries: never author useTweak in www/src/registry/ — the product source stays clean (the panel reuses registry UI, but the calls live only in site/feature/module code). It's throwaway scaffolding, not a /create axis: adding a real axis/variant/token is still a product decision (propose-and-approve — see CLAUDE.md).
• Cleanup: once the user picks (their "Copy for AI" output or a verbal choice), bake the values into the code and remove the useTweak scaffolding before finalizing the PR — unless they want to keep iterating. Don't merge useTweak calls into feature code.