feat(royalties): implement multi-recipient royalty splits for collaborative beats (#8)

[Simultech369]

Summary of Changes

This pull request resolves #8 by implementing multi-recipient royalty splits for collaborative beats, allowing beatmakers, vocalists, songwriters, and mixing engineers to automatically split on-chain license sales.

🎯 Key Implementations

1. Contract Interfaces & Split Math (src/contracts/crate.ts)

   • Defined strongly-typed RoyaltySplit interface (recipient, bps: basis points where 10,000 bps = 100%, role).
   • Added validateSplits helper enforcing 100% sum allocation (10,000 bps) and valid recipient addresses.
   • Added calculateSplitPayouts helper calculating pro-rata revenue allocations across collaborators while deterministically attributing fractional remainders to eliminate rounding drift.
   • Extended SampleData and uploadSample with splits?: RoyaltySplit[].

2. Upload UI with Dynamic Collaborator Splitting (src/pages/Upload.tsx)

   • Added dynamic collaborator rows allowing multiple contributor addresses, customizable roles (Producer, Co-Producer, Vocalist, Songwriter, Mixing & Mastering, Featured Artist), and percentage shares.
   • Quick-split presets: Solo (100%), 50/50 Split, and Equal Split.
   • Dynamic real-time allocation badge (green on 100% allocated, amber on remaining, red on exceeded) and validation preventing upload until total is 100%.
   • Live revenue breakdown preview displaying estimated XLM payouts per collaborator per sale.

3. Sample Detail & Profile Integration (src/pages/SampleDetail.tsx, src/pages/Profile.tsx)

   • SampleDetail.tsx: Displays collaborative royalty splits breakdown with role badges, recipient abbreviations, and percentage shares.
   • Profile.tsx: Displays individual contributor royalty shares and earnings on collaborative tracks, supporting per-collaborator withdrawal tracking.

4. Comprehensive Unit Tests (src/__tests__/royaltySplits.test.tsx)

   • 11 dedicated test cases verifying solo/multi-collaborator split validations, sum-to-100% boundary checks, basis points division, zero rounding drift, and error feedback.

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🧪 Verification & Testing

• npx vitest run: