fix: resolve /clear command and ESC key lag caused by hooks system

- Make hook events fire-and-forget in clearCommand to avoid blocking UI
- Move context.ui.clear() before resetChat for immediate responsiveness
- Add hasHooksForEvent() fast-path check to HookSystem and Config
- Skip MessageBus round-trips in client.ts when no hooks are registered
- Add comprehensive unit tests for all changes

Fixes #2651

packages/core/src/config/config.ts

@@ -1769,6 +1769,15 @@ export class Config {
     return this.hookSystem;
   }
 
+  /**
+   * Fast-path check: returns true only when hooks are enabled AND there are
+   * registered hooks for the given event name.  Callers can use this to skip
+   * expensive MessageBus round-trips when no hooks are configured.
+   */
+  hasHooksForEvent(eventName: string): boolean {
+    return this.hookSystem?.hasHooksForEvent(eventName) ?? false;
+  }
+
   /**
    * Check if hooks are enabled.
    */