EVM-56: Update README.md with EVM documentation

[Puneethkumarck]

Context

The project README needs to be updated to document EVM chain support, including supported chains, configuration options, API endpoints, and an updated architecture diagram reflecting the dual-chain capability of the indexer.

Specification

• EVM section in README.md covering:
  • Supported chains: Ethereum, Polygon, Arbitrum, Base (and any EVM-compatible chain)
  • Configuration: All EVM environment variables with descriptions and defaults
  • API endpoints: All 8 EVM REST endpoints with request/response examples:
    • GET /api/evm/stats
    • GET /api/evm/transactions (with filter params)
    • GET /api/evm/transactions/{txHash}
    • GET /api/evm/blocks (paginated)
    • GET /api/evm/blocks/{blockNumber}/transactions
    • GET /api/evm/transfers (with min_amount)
    • GET /api/evm/token-transfers (with token/from/to filters)
    • GET /api/evm/accounts/{address}
  • Architecture diagram: Updated to show the chain mode switch and EVM data flow path alongside the existing Solana path
  • Quick start: How to run in EVM mode with docker-compose
  • Chain-specific notes: Confirmation blocks, reorg depth, OP Stack deposits

Acceptance Criteria

• README.md contains an EVM section with all subsections listed above
• Supported chains listed with chain IDs
• All EVM environment variables documented with types and defaults
• All EVM API endpoints documented with example requests
• Architecture diagram updated to reflect dual-chain support
• Quick start instructions for EVM mode included
• Existing Solana documentation preserved (not removed or broken)

Dependencies

• EVM-49 through EVM-54: All E2E tests passing (EVM functionality verified before documenting)

References

• docs/evm-implementation-plan.md — Phase 7: EVM End-to-End & Documentation
• docs/evm-functional-spec.md
• docs/CODING_STANDARDS.md