chore(sync-service): initialize blockchain sync microservice

[mijinummi]

PR Description

This PR introduces the Blockchain Synchronization Service responsible for monitoring and synchronizing on-chain activities from the Stellar network. The service is designed as an independent NestJS microservice with support for real-time transaction monitoring, smart contract event listening, wallet balance synchronization, confirmation tracking, and webhook-based event notifications.

Features Implemented

• Initialized standalone NestJS blockchain sync microservice
• Added Transaction, Event, and Block entities
• Integrated Stellar Horizon API
• Implemented real-time transaction monitoring
• Added smart contract event listeners
• Implemented wallet balance synchronization
• Added block confirmation tracking
• Implemented webhook notification delivery
• Added transaction indexing foundation
• Configured Docker and Docker Compose setup

Technical Highlights

• Modular microservice architecture
• PostgreSQL persistence with TypeORM
• Scheduled blockchain polling and synchronization
• Environment-driven configuration
• Independent deployable service
• Scalable foundation for future indexing and streaming upgrades

Outcome

The service can independently monitor Stellar blockchain activity, persist synchronized data, track confirmations, and notify downstream systems through webhooks in real time.

Closes #313

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