TUI: show active model + reasoning effort in footer

Problem

When working across multiple Codex sessions/projects, it's easy to lose track of which model + reasoning effort each session is currently using—especially as developers increasingly switch reasoning levels for different phases (e.g. scoping/planning vs implementation vs review).

### Proposal
Add the current model slug and reasoning effort to the TUI footer, immediately to the left of the existing context indicator.

Example footer:
gpt-5.2 · high reasoning · 72% context left · ? for shortcuts

### Why this helps

• Makes the active session configuration visible at a glance.
• Reduces accidental "wrong effort" turns when context switching between sessions/projects.
• No change to API payloads or model selection behavior—purely a UI/status improvement.

### Behavior details

• Updates immediately when model/reasoning changes via /model.
• If reasoning effort is not explicitly configured, the footer shows the model's default effort (so it never shows "default").
• If a model has no reasoning effort, footer shows only the model name.

### Implementation sketch
Plumb model + reasoning_effort from ChatWidget → BottomPane → ChatComposer → FooterProps and render as a prefix in the footer line.

### Context
I saw the team's post inviting contributions here:
https://x.com/thsottiaux/status/1999980696534909144