TUI footer and statusline improvements

[Sachinv2223]

Feature Description

Two feature requests for the TUI:

1. Fixed footer panel — The input box and status area should stay pinned to the bottom of the terminal, like Claude Code's TUI. Currently it scrolls with
   content, which breaks the expected terminal app pattern.
2. /statusline command — A compact real-time footer showing active model name, context window usage (used/total %), current git branch, and session
   usage/credits. This exists as a user skill today but needs a native implementation since Command Code lacks Claude Code's statusLine config hook that streams
   session JSON on every turn.

Context threshold coloring would be useful: green (<70%), yellow (70–89%), red (≥90%). Git branch should gracefully handle non-repo directories

Use Case

No response

Additional Context

No response

How important is this to you?

None