feat: split bounty payouts across PR contributors

[iice257]

Summary

• derive payout recipients from the merged PR author plus linked GitHub commit authors/committers
• split the funded bounty amount evenly by cents across unique contributors
• persist one payout/activity event per recipient while keeping the existing single-recipient response fields for compatibility
• show a concise split-payout success message in the maintainer approval UI

Fixes #12.

Notes

This keeps the current single-recipient behavior when only one contributor is found. For multiple contributors, the primary PR author still gets PR-body wallet extraction; other contributors resolve through their connected GitHub account/email path or fall back to the existing unclaimed payout notification path.

Verification

• ./node_modules/.bin/tsc.cmd --noEmit
• ./node_modules/.bin/eslint.cmd app/b/[owner]/[repo]/issues/[issueNumber]/approve-button.tsx lib/api/client.ts lib/bounty/services/approve-payout.ts lib/bounty/payout-recipients.ts
• git diff --check

[vercel]

@iice257 is attempting to deploy a commit to the skndash96's projects Team on Vercel.

A member of the Team first needs to authorize it.

[bountic-bot]

⚡️ Bounty Competition Started

@iice257 has submitted a PR that references an issue with a bounty. Learn more about this bounty: https://bountic.vercel.app/b/skndash96/bountic/issues/12

When this PR is merged, the bounty will be locked and ready for payout approval.

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Bountic: Autonomous USDC bounties for open source