Mobile: group the new thread list by project instead of repeating the project name on every row

[ap-1325]

Where: mobile app (Android), Home thread list.

Problem. The new thread list shows the project name (with its icon) as the first line of every row. With one or two projects this line is the same on every card, takes a full row per thread, and pushes useful content down. The Legacy Thread List groups threads under a project header, which is much cleaner, but it lacks things the new list has, such as the provider logo on each row. Right now you have to choose between the two.

Proposal. Either of these would solve it:

1. A "Group by project" option in the new list (e.g. in the filter/sort menu): one project header per group with the thread count and the + new-thread button, and rows without the repeated project line. This mirrors the desktop grouping discussed in Sidebar: group the inbox by environment, project or provider — with rows that stop repeating themselves #7836, scoped to mobile.
2. At minimum, drop the project line from rows when it adds no information: when the list is filtered to one project, or when only one project exists.

Rows would keep the provider logo, status, time, and the environment · branch line.

Why it matters on a phone: vertical space is tight, and the repeated line roughly doubles the height of a card's metadata.

Related: #7836 (sidebar grouping, desktop), #10532 (compact sidebar), #6970 (mobile legacy parity).

[aaugmentum]

+1 from iOS. I run several repo projects plus a parent-folder project for cross-repo work. With 6+ projects, the flat list with a project line on every row makes it hard to scan. A "Group by project" option (or the legacy list's headers with the new row design) would fix it.