Add Human-in-the-Loop support

[double16]

What problem does this solve?

Current approach is fully automated. HITL is useful for guiding the agent, correcting direction, etc.

Proposed solution

1. Strands SDK has HITL support, leverage it.
2. Figure out how to integrate with stdin/stdout IPC.
3. HITL should be opt-in.
4. Emit an event for every HITL interaction.
5. Add HITL to React UI
6. Disable HITL for react --headless option
7. Running as a python process should default to HITL using stdin
8. Running as docker exec should default to HITL if stdin is a TTY.

Alternatives considered

No response

Which area does this affect?

Frontend/UI