Fix setup wrapper quoting for multi-word args

[ebbsanchez]

Fixes #94.

The setup-vouch wrapper was using Bash printf %q to build a Nushell command string. That escaping is shell-specific, so multi-word values such as custom commit messages or denounce reasons can be split or misparsed before reaching the Nushell command.

This changes the wrapper to quote arguments as Nushell double-quoted literals only when needed, while leaving command names and flags bare. It also escapes the resolved VOUCH_LIB_DIR path before embedding it in the use statement.

Verification:

• bash -n action/setup-vouch/vouch
• local wrapper smoke test with --reason "AI slop with spaces" --write, confirming the full reason was written as one value
• no-argument wrapper smoke test still prints usage
• nu tests/run.nu --fast
• git diff --check

[github-actions]

Hi @ebbsanchez, thanks for your interest in contributing!

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