feat(soroban): Create revenue sharing contract

[zeemscript]

Description

Implement a Soroban smart contract for automated revenue splitting between multiple parties. This enables transparent and automatic distribution of platform fees, educator payments, and affiliate commissions.

Acceptance Criteria

• Define revenue split percentages for multiple parties
• Automatic distribution of incoming payments
• Support for updating split percentages (with governance)
• Transparent on-chain record of all distributions

Files to modify/create

• contracts/revenue-sharing/src/lib.rs
• contracts/revenue-sharing/Cargo.toml
• src/modules/stellar/revenue-sharing.service.ts
• Integration tests for split calculations