fix(cli): preserve argument quoting for SingleCommand

[not-matthias]

Summary

• Replace naive args.command.join(\" \") with shell_words::join when reconstructing the command string for SingleCommand, so arguments containing spaces or shell metacharacters are properly quoted before being passed to the orchestrator.

Test plan

• cargo test
• Run codspeed run -- some-cmd 'arg with spaces' and confirm the argument is preserved as a single token.

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 7 untouched benchmarks

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_{Comparing fix/shell-words-join-single-command (8aecf2d) with main (e3dba09)}