Refine duck interaction and contributor prompt - #10

What changed

• Add a one-click prompt for contributing a Microduck policy.
• Require two successful angry quacks after stomping starts before the feet heat up.
• Shorten the post-click stomp cooldown.
• Replace hot-feet smoke rings with smaller, subtler animated SVG wisps.

Verification

• pnpm test
• pnpm build
• git diff --check