fix: reusable agent after stop

Reset AbortController and status when stop() is called.
Agent can now be reused for subsequent tasks.

Changes:
- Check if already stopped to prevent double-abort
- Reset status to 'idle'
- Create new AbortController for next task

packages/core/src/PageAgentCore.ts

@@ -187,9 +187,12 @@ export class PageAgentCore extends EventTarget {
 
 	/** Stop the current task. Agent remains reusable. */
 	stop() {
+		if (this.#abortController.signal.aborted) return // Already stopped
 		this.pageController.cleanUpHighlights()
 		this.pageController.hideMask()
 		this.#abortController.abort()
+		this.#setStatus('idle')
+		this.#abortController = new AbortController()
 	}
 
 	async execute(task: string): Promise<ExecutionResult> {