Feature request: Show running agents in status line with click-to-focus

Summary

When Claude Code launches subagents to complete tasks, there's no easy way to monitor their activity in real time. It would be great if the status line could show a list of currently running agents, and clicking on one would open/focus a terminal view showing that agent's live output.

Current behavior

• Status line shows static metadata (model, context, cost, git branch)
• No agent-related data is available in the status line JSON
• Users must manually expand inline blocks or tail transcript files to monitor agents

Proposed behavior

• Status line displays active agents (e.g., [Agent 1: searching...] [Agent 2: editing...])
• Clicking/selecting an agent opens or focuses its terminal output
• Visual indicators for agent states (running, idle, completed)

Motivation

As agents become more central to the workflow, visibility into what they're doing is essential for trust and productivity.