refactor(plugin): remove metadata assertions

Guard optional plugin metadata and pane identifiers before passing them to cleanup and warning paths.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/plugin-handlers/command-config-handler.ts

@@ -43,8 +43,8 @@ export async function applyCommandConfig(params: {
   const includeClaudeSkills = params.pluginConfig.claude_code?.skills ?? true;
 
   const externalSkillPlugin = detectExternalSkillPlugin(params.ctx.directory);
-  if (includeClaudeSkills && externalSkillPlugin.detected) {
-    log(getSkillPluginConflictWarning(externalSkillPlugin.pluginName!));
+  if (includeClaudeSkills && externalSkillPlugin.detected && externalSkillPlugin.pluginName) {
+    log(getSkillPluginConflictWarning(externalSkillPlugin.pluginName));
   }
 
   const [