Add Solana Chain Watcher with onLogs subscription for SPL Token transfers

[geminimir]

Summary

Add Solana chain monitoring using @solana/web3.js. Subscribe to onLogs for the USDC SPL Token program (EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v).

Changes

• Solana WebSocket connection via @solana/web3.js
• onLogs subscription filtered to USDC token program
• Parse SPL Token Transfer instructions for amount, sender, receiver
• Store with chain=solana in chain_transactions

Tests

• Mocked Solana transfer log is detected and stored
• Non-USDC token transfers are ignored

Acceptance Criteria

Solana USDC transfers are monitored in real-time.