Desktop app: bring back the context-usage indicator (or make the footer widget configurable)

The desktop app's bottom-right footer currently shows the 5-hour usage-limit ring. Earlier builds showed context-window usage there. For long agentic sessions the context number is the more actionable one (am I approaching compaction?), while the usage ring rarely changes any decision mid-session.

Request, in order of preference:

1. Show context usage in the footer again, or
2. Make the footer widget configurable (context, usage, or both), or
3. Honor the existing statusLine setting from settings.json in the desktop chat view, which would solve this generically.

Currently statusLine only renders in terminal sessions, so desktop users have no persistent context display at all. /context works but is on-demand only.

Environment: Windows 11, Claude Code desktop app, latest update channel.