fix(ai): resolve engine aliases in pickAiEngine

pickAiEngine() passed the raw preferred string directly to ENGINES lookup,
so aliases like 'cc' for claude or 'openai' for codex were never resolved.
Fixed by calling resolveEngine() first, matching all other CLI surfaces.

Author: Nivokvo Bounty Hunter

src/engines.mjs

@@ -155,7 +155,8 @@ export function aiExecArgs(engine, prompt) {
 
 /** First installed engine that supports headless ai(), honoring a preference. */
 export function pickAiEngine(preferred) {
-  const order = preferred ? [preferred] : ["claude", "codex", "opencode", "gemini", "aider"];
+  const resolved = preferred ? resolveEngine(preferred)?.[0] : null;
+  const order = resolved ? [resolved] : ["claude", "codex", "opencode", "gemini", "aider"];
   for (const key of order) {
     if (Object.hasOwn(ENGINES, key) && Object.hasOwn(AI_EXEC, key) && isInstalled(ENGINES[key].bin)) return key;
   }