Mobile: show the thread's provider limits (remaining + time to reset) and context in the thread overflow menu

[ap-1325]

Where: mobile app (Android), thread screen.

Problem. On a phone there is no glanceable way to see, inside a chat, how much of the subscription behind that chat is left. /usage-limits works, but you have to type it every time, and the context window meter from desktop is missing on mobile. Codex Remote shows this in the chat's overflow menu, and that is the habit many of us bring over.

Proposal. In the thread header overflow menu (⋮, currently "Open terminal" / "Open git controls"), add a small read-only section for the thread's selected provider instance:

• 5-hour window: remaining % and time to reset, e.g. 5h · 24% left · resets in 39m
• Weekly window: remaining % and days to reset, e.g. Week · 94% left · resets in 3d
• Context window: % free for this thread, e.g. Context · 81% free
• Tapping the section opens the existing /usage-limits panel for details.

The data already exists: the server's usage limit sources (the same report /usage-limits uses, including reset times) and the thread's context-window.updated activity. So this is mostly client work, scoped to the selected thread's provider, so a Codex chat shows Codex limits and a Claude chat shows Claude limits.

Why the menu rather than the header: the phone header truncates quickly, and the menu keeps it out of the way until needed.

Workaround we use today. A server-side timer renames the project every 20s with t3 project rename to e.g. 39m 24% · 3d 94% · content, which shows up under the thread title on Android. It works, but it is shared by all threads, it shows the most recently active thread's provider rather than the open one, and it writes a project event on every change. A native per-thread view would remove the need for this.

Related: #10336 (context meter on the phone), #6954 (mobile context ring), #11891 (composer usage meter), #11563 (5h/weekly in the top bar).