#18938: fix(completion): avoid compdef error in zsh by guarding completion init

## Summary - fix `command not found: compdef` for zsh users with minimal shell setup - make generated zsh completion source block interactive-only - ensure `compinit` is available before sourcing cached completion script ## What changed In `src/cli/completion-cli.ts`, `formatCompletionSourceLine(...)` now emits this for zsh: ```zsh if [[ -o interactive ]]; then autoload -Uz compinit (( $+functions[compdef] )) || compinit source "<cache-path>" fi ``` ## Why The previous install block only sourced the completion script. In shells where `compinit` had not run yet (common in minimal/clean `~/.zshrc` setups, especially over SSH), the script's `compdef` calls failed. ## Notes - behavior for bash/fish is unchanged - this preserves completion behavior for interactive shells while avoiding startup errors in non-interactive contexts <!-- greptile_comment --> <h3>Greptile Summary</h3> Fixed `command not found: compdef` error in zsh by wrapping completion initialization in an interactive-only guard that ensures `compinit` is loaded before sourcing the cached completion script. - Wrapped zsh completion source block with `[[ -o interactive ]]` check - Added `autoload -Uz compinit` to load the completion system - Added `(( $+functions[compdef] )) || compinit` to initialize only if `compdef` is missing - Prevented startup errors in non-interactive contexts (e.g., SSH sessions, minimal `.zshrc` setups) <h3>Confidence Score: 5/5</h3> - Safe to merge - addresses a specific zsh initialization error with a standard solution - The fix follows zsh best practices by checking for interactive mode, loading compinit only when needed, and preserving bash/fish behavior. The implementation is minimal, targeted, and uses standard zsh idioms (`[[ -o interactive ]]`, `autoload -Uz`, `$+functions[compdef]`). No behavior changes for other shells. - No files require special attention _{Last reviewed commit: e145af6} <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->