Mobile haptics for Bungkus checkout

Add meaningful, accessible haptics to the Bungkus receipt-splitting checkout flow. Three haptic events minimum: item added, payment submitted, payment confirmed. Respect iOS and Android haptic guidelines and the user's reduce-motion setting.

<rubric>

• ·3 distinct haptic events in the checkout flow
• ·Respects system reduce-motion setting on both platforms
• ·No regression in the existing haptics (if any)
• ·Documented in code with accessibility rationale

<how claims are judged>

We'll test on a real iPhone 15 and a Pixel 8. The PR ships if the rubric holds and accessibility review is clean.

<submission format>

curl -X POST https://api.uthm-forge.dev/bounties/4/claim \
  -H "Authorization: Bearer $UTHM_TOKEN" \
  -d '{"repo":"github.com/you/bungkus-haptics","pr":3}'