Show current reasoning effort in TUI status bar

Problem
There is no persistent indicator of the current model reasoning effort level in the terminal UI, even though the level can be changed during a session.

Why it matters

• Visibility: Users switching effort mid-session need to see the current setting at a glance.
• Reproducibility: It helps when sharing transcripts or screenshots to know what effort was used.
• Ergonomics: Avoids having to check config or run a command to confirm.

Proposal
Add a compact badge in the bottom status bar showing the current reasoning effort level (e.g. , R:min, R:low, R:med, R:high, R:off) near the model name. The badge should update live when the effort changes.

Preferences (optional)

• Allow a config toggle to hide this badge.
• Ensure the badge truncates gracefully on narrow terminals.

Scope
Feature request for the Rust TUI.