Mobile background-work pill shows only a count; web lists each item #21342

When a thread is waiting on background work, the web chat banner lists every item (each monitor, command, subagent, or background task by name). The mobile app shows only the summary pill, for example "Waiting on 4 monitors", and tapping it does nothing. There is no way on mobile to see what the thread is actually waiting on.

Mobile already computes the item names with the same shared helper as web (presentPendingBackgroundWork in packages/client-runtime). It uses them only for the pill's accessibilityLabel (apps/mobile/src/features/threads/ThreadDetailScreen.tsx), so screen reader users hear the list but sighted users can't see it.

Steps

1. Start a turn that leaves several monitors or background commands running.
2. Open the thread on web: the banner lists each item.
3. Open the same thread on mobile: the pill says "Waiting on N monitors" and can't be opened.

Expected: mobile shows the same items as web.