cn commands: use omarchy-cmd helpers per bin style rule

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QKxGW1raAWaqeU8WdHsMsp

bin/omarchy-cn-ai-launch

@@ -20,7 +20,7 @@ model=$(cn_ai_profile_field "$profile" model)
 command=$(cn_ai_harness_field "$harness" command)
 config_method=$(cn_ai_harness_field "$harness" config_method)
 
-if ! command -v "$command" > /dev/null 2>&1; then
+if omarchy-cmd-missing "$command"; then
   install=$(cn_ai_harness_field "$harness" install)
   if [[ $install == doc:* ]]; then
     echo "$harness 未安装，安装方法见官方文档: ${install#doc:}" >&2