Add addGroupCommandWithReplies() to AgentRegistryService that sends commands
to all LIVE agents in a group and returns CompletableFuture per agent for
collecting replies. Update sendGroupCommand() and pushConfigToAgents() to
wait with a shared 10-second deadline, returning CommandGroupResponse with
per-agent status, timeouts, and overall success. Config update endpoint now
returns ConfigUpdateResponse wrapping both the saved config and push result.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>