feat: add stop cmd

[aspnxdd]

Closes #629

Add stop command that internally does an RPC request with "exit" - better UX

surfpool stop

I also tried the stop command in the PR #704 and it works with the --daemon flag : it stops the process.

[greptile-apps]

Greptile Summary

This PR adds a surfpool stop command for requesting a running instance to exit.

• New stop CLI subcommand with a configurable RPC URL.
• JSON-RPC exit request sent to the selected endpoint.
• Bounded HTTP client timeout for the stop request.
• Response validation for JSON-RPC version, request id, result, and RPC errors.
• Tests for stop command parsing and response handling.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
crates/cli/src/cli/mod.rs	Adds the stop command, sends a bounded JSON-RPC exit request, validates the response shape, and covers the main parser and response cases with tests.

_{Reviews (4): Last reviewed commit: "Update crates/cli/src/cli/mod.rs" | Re-trigger Greptile}