Approves and executes a pending action proposed by the agent.
When confirmed, the system dispatches the execution logic (e.g., posting a reply to GitHub) based on the action's source_type and tool_name, and then updates the action status to executed.
If the action requires a mapping that is missing (e.g., suggesting a GitHub issue type without mapping), it returns a 400 error with error_code: mapping_required and includes available mapping options.