feat(agent): handle max iteration exceeded gracefully in ReAct agent

**Background**

When a ReAct agent exceeds the maximum number of iterations, it currently terminates the loop abruptly. A more graceful handling strategy should be introduced to improve the user experience.

**Proposed Solutions**

Two approaches are under consideration:

1. **Summarization**: guide the agent to summarize its progress and generate a final text response before exiting.
2. **Human-in-the-loop**: emit an event to the frontend, letting the user decide whether to continue. If allowed, either increase the iteration limit or reset the iteration counter and resume the ReAct loop.