feat: implement On-Chain Event Correlation Service

[nazteeemba]

Closes #546

Summary

Implements the On-Chain Event Correlation Service — a NestJS module that automatically fetches Soroban smart contract events, maps them to internal AidPackage and Claim records by package_id/claim_id, and persists the mapping (tx hash, ledger, event topic) idempotently. Correlated events are surfaced on the claim and package read endpoints.

Changes

New files

File	Description
prisma/migrations/.../migration.sql	Creates OnChainEvent and CorrelationCursor tables with unique index and 4 query indexes
src/onchain/event-correlation/event-mapper.ts	Pure EventMapper — decodes ScVal topics/values, extracts package_id/claim_id, DB lookups, full error handling
src/onchain/event-correlation/event-correlation.service.ts	correlate() with cursor-based ledger resumption, @Cron scheduler (every 5 min), isRunning concurrency guard
src/onchain/event-correlation/event-correlation.controller.ts	POST /v1/onchain/events/correlate — on-demand trigger with ledger validation, HTTP 502 on RPC failure
src/onchain/event-correlation/dto/correlation-result.dto.ts	CorrelationResult interface

Modified files

File	Change
prisma/schema.prisma	Added OnChainEvent and CorrelationCursor models
src/onchain/onchain.module.ts	Registered EventMapper, EventCorrelationService, EventCorrelationController
src/onchain/aid-escrow.controller.ts	GET /onchain/aid-escrow/packages/:id returns onChainEvents array
src/onchain/aid-escrow.module.ts	Added PrismaService to providers
src/claims/claims.service.ts	findOne includes onChainEvents array (always present, empty when no events)

Acceptance criteria

• Correlation runs on-demand via POST /v1/onchain/events/correlate
• Correlation runs automatically on a 5-minute cron schedule
• Correlated data exposed on GET /v1/claims/:id and GET /onchain/aid-escrow/packages/:id
• Mapper logic covered by unit tests (P1–P4 property tests + E1–E10 example tests)

Testing

# From app/backend/
npx prisma migrate deploy
npx jest --testPathPattern="event-mapper|event-correlation" --run

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