feat!: Refine lifecycle hooks; fix abortSignal

- add `stop` method. agent can be reused after stopped
- agent can not be reused after disposed
- extension DO NOT exposes `dispose` anymore. only `stop`.
- update panel for new `stop` method
- fix MultiPageAgent dispose event
- better handling abortSignal

packages/extension/src/agent/useAgent.ts

@@ -84,7 +84,7 @@ export function useAgent(): UseAgentResult {
 	}, [])
 
 	const stop = useCallback(() => {
-		agentRef.current?.dispose()
+		agentRef.current?.stop()
 	}, [])
 
 	const configure = useCallback(async (newConfig: LLMConfig) => {