fix(shell): avoid full mise hook on server zsh

[shunk031]

Why

Server-side Zsh startup paid the full mise activate zsh hook cost even though server startup only needs the standalone mise binary and shims. Measurements showed _mise_hook / mise hook-env -s zsh cost about 40-50 ms, while the server prompt setup should remain unchanged.

What Changed

• Move full eval "$(~/.local/bin/mise activate zsh)" from the common Sheldon config to the client-only Sheldon config.
• Add a Zsh startup helper that exposes mise and shims via mise activate zsh --shims without registering _mise_hook, precmd, or chpwd hooks.
• Source the Zsh helper from the server Sheldon config before Starship, keeping Starship unchanged.
• Replace the static .zprofile source with a template that uses shims-only startup on servers and full mise activation elsewhere.
• Extend install tests to cover the Zsh helper, Sheldon client/server split, and .zprofile template behavior.
• Isolate Zsh startup tests from bashcov tracing variables so CI output checks remain deterministic.

Validation

Inspect the diff for whitespace errors.

git diff --check

Parse the Zsh mise helper.

zsh -n home/dot_config/exact_shell/mise.zsh

Render the server .zprofile template and parse it as Zsh.

chezmoi execute-template --override-data '{"system":"server"}' < home/dot_zprofile.tmpl | zsh -n

Render the client .zprofile template and parse it as Zsh.

chezmoi execute-template --override-data '{"system":"client"}' < home/dot_zprofile.tmpl | zsh -n

Parse the mise install shell sources.

bash -n install/common/mise.sh home/dot_config/exact_shell/mise.bash

Run ShellCheck for the mise install shell sources.

mise exec -- shellcheck install/common/mise.sh home/dot_config/exact_shell/mise.bash

A temp-HOME Zsh smoke test confirmed fake mise and a shimmed chezmoi are found, and _mise_hook is absent from functions, precmd_functions, and chpwd_functions.

Local bats tests were not run per repository policy; GitHub Actions should validate them.