refactor: remove arbitrum cli dependency

[alxdca]

Summary

• Replace arbitrum deploy generate-config calls with in-process node config generation via @arbitrum/chain-sdk.
• Add @arbitrum/chain-sdk as a package dependency and update rollup deployment helpers to import SDK APIs directly.
• Remove the arbitrum exec wrapper, its CLI-dependent test, and the README dependency note for the external arbitrum CLI.

Why / Context

• The init flow should not require a separately installed arbitrum CLI to generate L2/L3 node configs.
• Using the chain SDK directly keeps rollup deployment and config preparation inside the Node runtime.
• This also removes the previous local SDK build/entrypoint assumption from src/sdk-chain.ts.