[FEATURE REQUEST] Show context usage indicator in the iOS app (parity with web)

Feature description

The web interface (claude.ai/code) shows how much of the model's context window the current session is using. The iOS app has no equivalent indicator.

Why it matters

When driving long-running sessions from the phone (e.g. remote-controlling a session started elsewhere), there is no way to tell how close the session is to auto-compaction. Context usage affects when to wrap up a task, when to expect a summary/compaction to kick in, and whether it is safe to hand the session a large new instruction. On web this is visible at a glance; on iOS you are flying blind.

Suggested behavior

Show the same context usage indicator the web UI already has (percentage or fraction of the context window used), e.g. in the session header or the session info sheet.

Environment

• Claude iOS app (Claude Code session view)
• Same session viewed on claude.ai/code shows the indicator