feat: add self-update/upgrade command to CLI

[amilz]

Summary

Add a self-update command to the Surfpool CLI (e.g. surfpool update or surfpool upgrade) that checks for the latest release and updates the binary in place.

Motivation

Modern CLIs like bun upgrade and claude update provide a frictionless self-update experience. Surfpool should offer the same — users shouldn't need to manually download new releases or re-run an install script.

Proposed Behavior

• surfpool update — check for the latest GitHub release, download and replace the current binary if a newer version is available
• If already on the latest version, print a message and exit
• Show download progress
• The command should appear in the --help menu

Acceptance Criteria

• New update (or upgrade) subcommand added to the CLI
• Checks latest release from GitHub releases API
• Downloads and replaces the running binary on update
• Prints current version vs. latest version
• No-op with friendly message when already up to date
• Visible in surfpool --help output

[VivekJaiswal18]

Can I work on this @MicaiahReid ?

[MicaiahReid]

Yeah, go for it @VivekJaiswal18! As a note, there is an install.sh file in the repo that powers the normal install script, I wonder if this could be utilized but haven't thought it through much.

[VivekJaiswal18]

@MicaiahReid should we also add a command to download specific versions directly from the cli by passing the versions to it?

[MicaiahReid]

Yeah, I think that would be great!