feat(devnet): add docker-compose for local devnet + docs

[skyc1e]

Problem

Developers need a zero-friction way to spin up a local RPC/WS node for quick testing (curl, websockets, txpool) without running a full multi-process stack.

Solution

• Added docker-compose.devnet.yml to run a single geth-based dev node with HTTP(8545) and WS(8546).
• Added docs/devnet.md with a 1-minute quickstart and smoke tests.

How to test

docker compose -f docker-compose.devnet.yml up --build
curl -s -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  --data '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'
# or run node ws-test.mjs from docs

[skyc1e]

ayo team 👋
This PR adds a minimal docker-compose.devnet.yml setup and a short docs/devnet.md guide to make it easier for new devs to spin up a local MegaETH node for quick RPC/WS testing.

Verified locally -- both endpoints respond (eth_blockNumber + WS subscription).

Let me know if you'd like me to add a simple CI smoke test (run compose + curl check) in a follow-up PR