[FEATURE] Mobile: persistent indicator for context in use + 5h and weekly usage (re-file of stale-closed #71583)

### Problem Statement

On Claude Code mobile there is no persistent readout of where a session stands. Two separate things are invisible while you work:

1. **Context in use** — how full the context window is.
2. **Quota consumed** — how much of the current 5-hour window and of the weekly allowance has been spent.

The terminal CLI keeps a context indicator in view. Mobile keeps nothing in view, so the only way to learn either number is to stop and ask, and the usage windows in particular are buried in menus rather than reachable from the session at all. You find out you are near a limit by hitting it, mid-task, on the surface where recovering is hardest.

### Proposed Solution

A small always-visible indicator during a mobile session — an icon or compact badge, not a panel — carrying three numbers:

- context in use (e.g. `120k/200k` or a percentage)
- current **5-hour window** usage
- current **weekly** usage

Tapping it expands to the full breakdown. Placement can reuse chrome that is already on screen (the existing session action affordances) rather than claiming new real estate — see #76794, which makes that argument well for the context half.

### Why this is not already covered

The context-window half of this has two open requests: #76794 and #87722. Neither covers the 5h or weekly usage windows.

The usage half was requested in #71583, which was **auto-closed as inactive on 2026-08-12 by the stale bot, not declined** — its closing comment reads "Please open a new issue if this is still relevant." It is still relevant. This is that re-file, narrowed to the part no open issue currently tracks.

### Use Case

Driving a session from a phone, away from the desk, part-way through a task. Deciding whether to send a large prompt, kick off a long agent run, or stop and pick it up later depends entirely on how much 5h and weekly budget is left. Right now that decision is made blind, and the failure mode — running out mid-run on mobile — is the expensive one.

### Priority

Medium-high — it does not block work, but it makes the mobile surface unpredictable to plan around.

*Filed by the user's Claude Code session on their behalf, at their request.*

Start by reviewing the related requests #76794 and #87722, along with the re-filed usage request #71583. Then inspect the mobile session's existing action affordances and usage menus; done means a session exposes context, 5-hour, and weekly usage indicators with an expanded breakdown available by tapping.

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