Show model name for each entry in the background task list

Feature request

In the background task/agent list (the compact view showing each running task as <agent-name> <current activity description> <elapsed time> · <token usage>, e.g.:

main
app-dev-director   Fixing grid re-enable in m6-verify.mjs   22m 55s · ↓ 193.7k tokens
general-purpose    Checking SPEC-UI.md heading structure     3m 46s · ↓ 78.8k tokens

It would be helpful to also show which model each task/agent is running on (e.g. [opus] / [sonnet] / [haiku]), especially when using per-agent model overrides. This makes it easier to see at a glance which subagents are on which model tier without having to inspect each one individually.

Motivation

When delegating work to multiple subagents with different model overrides (e.g. a cheaper model for simple mechanical tasks, a stronger model for design/judgment work), it's currently not visible from the task list which model each entry is actually using.