Mobile: a nav bar button that jumps the thread list to the Working shelf

[YazanKittaneh]

Problem

On mobile, the Working shelf sits below every pinned and active thread on the home list. With a busy inbox, checking on running agents means a long scroll every time, and the shelf is collapsed by default, so you land on a closed header and have to tap again.

Proposal

Add a button to the top nav bar of the mobile thread list, next to search, that scrolls the list to the Working shelf and expands it if it is collapsed.

• It appears only while the list has a Working shelf, so it never sits there doing nothing. It hides while searching and on other tabs.
• iOS: a toolbar item in the workspace header. Android: an icon button in the home header row, beside search.
• It reuses the shelf's existing expand preference, so expanding it this way is the same as tapping the header.

Scope

Mobile only, home thread list only. No contract, server, or settings changes. Web and desktop already show the Working shelf in the sidebar, where it is easier to reach, so I'm not proposing a change there.

I have a small implementation ready (6 files in apps/mobile, about 70 lines) and would open a PR, with before/after screenshots, if this direction looks right. Happy to change the placement or the icon, or to drop the auto-expand.