Implement update_royalty_split Function with Admin Authorization

[syed-ghufran-hassan]

Description

This PR implements the missing update_royalty_split function that was referenced in GitHub Issues #80 and #81. Previously, admins had no way to update royalty splits once the contract was deployed. This PR adds the functionality with proper admin authentication and input validation.

Closes Issue: # #626

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🛠️ Stack Checklists

Please fill out the checklist(s) relevant to your changes. You can delete the sections that do not apply.

🖥️ Frontend (Next.js / React)

• Responsive Design: Checked UI on mobile, tablet, and desktop views.
• State Management: Verified that local state or context updates don't cause infinite re-renders.
• Error Handling: Form inputs and API calls have proper validation, loading states, and user-facing error messages.
• Accessibility: Interactive elements have proper aria labels, roles, and keyboard navigation.

⚙️ Backend Indexer (Node.js / Prisma)

• Database Migrations: If Prisma schema changed, I generated and committed the migration file.
• Reorg Safety: If adding a new event listener, I ensured revertLedgers properly rolls back the state on ledger reorgs.
• Performance: Avoided N+1 query problems in API routes; used proper indexes for new Prisma models.

⛓️ Smart Contracts (Soroban / Rust)

• TTL Extensions: If I modified Persistent storage, I explicitly called extend_ttl immediately after setting.
• Instance TTL: I ensured extend_instance_ttl is called if this is a public, state-modifying entry point.
• Authorization: Verified that require_auth() is used correctly and doesn't block approved operators.
• Gas Efficiency: Avoided storage reads/writes or .get(i).unwrap() host calls inside loops.
• State Bloat: Avoided unbounded Vec arrays for global state tracking.

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🧪 Testing & CI

• I have added unit or E2E tests to cover my changes and edge cases.
• All tests pass locally (cargo test, npm run test, or npx playwright test).
• I have run the linter and code formatter locally before pushing.

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Additional Context

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