feat: implement settlements repository (#17)

[Chucks1093]

Closes #17

Summary

Implements a complete settlements persistence layer with Prisma, including schema, migration, repository methods, and isolated unit tests.

Changes

• Added prisma/schema.prisma with:
  • Settlement model
  • SettlementStatus enum: pending | completed | failed
• Added Prisma migration to create the settlements table with indexes on:
  • developerId
  • status
• Added src/db.ts as a Prisma client singleton
• Added SettlementRepository with all required methods:
  • create(developerId, amountUsdc, status)
  • findById(id)
  • listByDeveloper(developerId, limit, offset)
  • updateStatus(id, status, txHash)
    • Enforces txHash for completed
    • Sets completedAt and stellarTxHash on completion
    • Clears completion metadata for non-completed statuses
  • getPendingSettlementTotal(developerId)
    • Returns decimal string total
    • Returns "0" when no pending settlements exist
• Renamed jest.config.js to jest.config.cjs to resolve ESM/CJS config loading conflict

Testing

• Added full unit test coverage using jest-mock-extended (no real DB required)
• Covered:
  • Create behavior (default and explicit statuses)
  • findById found/not-found paths
  • listByDeveloper pagination and ordering
  • updateStatus transitions and validation edge cases
  • Aggregate behavior in getPendingSettlementTotal including empty/null sums
• Verified locally:
  • npm run typecheck
  • npm test

[Chucks1093]

@greatest0fallt1me please can you quickly merge this .thanks

[greatest0fallt1me]

please resolve the conflicts

[Chucks1093]

@greatest0fallt1me

[greatest0fallt1me]

@Chucks1093 Can you resolve the conflicts?