fix(completions): apply compdef guard during zsh generation

Instead of hand-patching the generated ironclaw.zsh file (which is
fragile and lost on regeneration), patch the compdef call in the
generation code itself. The Zsh output is post-processed to wrap
`compdef _ironclaw ironclaw` with a `$+functions[compdef]` guard.

Regenerated ironclaw.zsh from the patched code to stay in sync.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: zmanian