fix(pty-proxy): resolve bare zsh interpreter path in init guard

[davidolrik]

A smaller fix for #3606 that resolves a bare ssh to its full path.

Checks

• I am happy for maintainers to push small adjustments to this PR, to speed up the review cycle
• I have checked that there are no existing pull requests for the same thing

[greptile-apps]

Greptile Summary

This PR resolves bare zsh interpreter names before starting the PTY proxy. The main changes are:

• Resolve non-absolute ZSH_ARGZERO values through PATH.
• Forward the resolved path to atuin pty-proxy.
• Update init-script assertions for the new logic.

Confidence Score: 4/5

Relative zsh interpreter paths can select the wrong binary and need correction before merging.

• Bare zsh values are resolved as intended.
• Relative paths such as ./custom/zsh are discarded instead of resolved.
• The proxy can start a different zsh from the one that loaded the init script.

crates/atuin-pty-proxy/src/pty_proxy.rs

Important Files Changed

Filename	Overview
crates/atuin-pty-proxy/src/pty_proxy.rs	Adds zsh path resolution, but replaces valid relative interpreter paths with a potentially different binary from PATH.

_{Reviews (1): Last reviewed commit: "fix(pty-proxy): resolve bare zsh interpr..." | Re-trigger Greptile}