Feature Request: Display custom agent name in CLI spinner when using Agent tool

Problem

When spawning agents via the Agent tool with a name parameter, the CLI spinner/status line shows generic "Agent" text. The name parameter works correctly for SendMessage routing between agents but never surfaces in the UI.

Current Behavior

• Spinner shows: Agent (generic)
• agent.name field in status line JSON: only populated when running with --agent CLI flag, not for Agent tool invocations
• No way to distinguish between multiple running background agents in the UI

Requested Behavior

1. Propagate the Agent tool name parameter to the realtime spinner display so users can distinguish between multiple running agents
2. Populate the agent.name field in the status line JSON for Agent tool invocations, not just --agent CLI flag sessions
3. Fallback to description parameter if name is not set

Use Case

Multi-agent workflows where several named agents run across parallel phases. Users need to know which named agent is currently active in the spinner rather than seeing generic "Agent" for all of them.

Environment

• Claude Code CLI on native Ubuntu
• Using Agent tool for multi-phase workflows with multiple background agents running simultaneously