feat: track latest current block of chain

[longhoangwkm]

Summary

Adds current_block_no field to processed_blocks table to track the latest blockchain head, enabling monitoring of block processing delays.

Key Changes

• Database Schema: Added current_block_no column to processed_blocks entity with migration
• Block Scanning: Updates current_block_no when fetching current blockchain state during scan cycles
• Documentation: Comprehensive README rewrite with:
  • Architecture diagrams and data flow
  • Microservice integration guide with RabbitMQ examples
  • Event configuration documentation
  • Setup and deployment instructions
• Example Config: Added events.seed.example.json showing event configuration patterns
• Tests: Updated test assertions to verify current_block_no tracking

Why This Matters

Enables monitoring of the gap between processed blocks (block_no) and current chain head (current_block_no), providing visibility into:

• Scanning lag/delays
• System health and catch-up progress
• Real-time vs. historical processing status