Add Ethereum account monitoring tool

[Copilot]

Implements real-time monitoring for Ethereum accounts via Etherscan API, complementing existing Bitcoin P2P and mempool monitors.

Implementation

Core Monitor (monitor-accounts.js)

• Continuous polling with configurable intervals (default: 60s, min: 10s)
• Tracks ETH balance and last 5 ERC20 token transfers per address
• Detects new transactions by comparing hash chains
• Console UI with transaction direction indicators (⬇ IN / ⬆ OUT)
• Multi-address support in single process

Testing (test-monitor-accounts.js)

• 21 unit tests covering token formatting, Wei conversion, address validation
• Demo script showing expected output format

Documentation

• Complete usage guide with troubleshooting
• Rate limit considerations for Etherscan API

Usage

# Single address
ETHERSCAN_API_KEY=key node contrib/devtools/monitor-accounts.js 0xAddress

# Multiple addresses, custom interval
POLL_INTERVAL=30 ETHERSCAN_API_KEY=key node contrib/devtools/monitor-accounts.js 0xAddr1 0xAddr2

Output Format

Address: 0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb0
  ETH Balance: 5.234567 ETH
  Status: 🔔 NEW TRANSACTION DETECTED!

  Recent Token Transfers:
  1. ⬇ IN  | 100.000000 USDT
     Block: 19123456 | 2026-02-16T05:40:00.000Z

Technical notes:

• Zero external dependencies (uses Node.js built-ins only)
• Etherscan API V2 for Ethereum mainnet (chain ID 1)
• Promise-based async with proper timeout handling

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