feat: support split bounty payouts

[Christayc]

Fixes #12.

Summary

• add multi-recipient payout resolution for merged bounty PRs
• support explicit PR-body recipient wallet tags plus weighted split tags
• fall back to commit-author weighted splits when no explicit split is provided
• preserve exact payout totals with integer-cent allocation
• persist payout and activity rows per recipient while keeping the existing single-recipient response compatible
• update maintainer approval messaging, README, LLM docs, and Locus mock email payout support

Validation

• pnpm install --frozen-lockfile --ignore-scripts
• pnpm typecheck
• eslint on touched TypeScript/TSX files
• git diff --check

Full pnpm lint still reports pre-existing unrelated lint errors in app/mock-checkout/[checkoutId]/page.tsx and app/page.tsx, plus unrelated warnings. The files touched by this PR pass focused ESLint.

[vercel]

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[bountic-bot]

⚡️ Bounty Competition Started

@Christayc 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