feat(backend): Implement event indexing service for pool creation

[rafamiziara]

Overview

Create shared event indexing service to parse PoolCreated events and store pool data in Firestore.

Tasks

• Create services/eventIndexer.ts with shared pool indexing logic
• Implement parsePoolCreatedEvent() to extract pool data from events
• Implement storePoolInFirestore() with idempotency checks
• Create utils/blockchain.ts with ethers.js helpers
• Implement getTransactionReceipt(), getLatestBlockNumber()
• Add error handling for RPC failures

Acceptance Criteria

• Service successfully parses PoolCreated events
• Idempotent storage prevents duplicate pools
• Handles all supported chains (Polygon Amoy, localhost)
• Comprehensive error handling for blockchain interactions

Related Documentation

• See docs/POOL_CREATION_ARCHITECTURE.md Phase 4
• See docs/POOL_CREATION_TASKS.md Tasks 3, 6

Labels: comp: backend, type: feature

Milestone: Sprint 3: Pool Creation

Part of Epic: #35