TUI: DialogModel is too narrow and truncates model names

Description

In the TUI, the model selection dialog (DialogModel) remains locked to the default "medium" width (60 columns) regardless of terminal window size.
When models have descriptive names or when providers include additional backend info in the footer (e.g. custom endpoints, vLLM / Ollama instances, OpenRouter model variants), the footer consumes 35-45 columns. In a 60-column dialog, this leaves only ~15 characters for the model name, causing heavy truncation (e.g., Gemma 4 12B cod..., GPT-OSS 20B (Op...).

Steps to reproduce

1. Configure custom models or providers with descriptive names / footers.
2. Open the model picker in TUI (/models or shortcut).
3. The dialog only uses 60 columns even on wide (120-200 col) terminals, truncating model names.

Operating System

Linux x86_64

Terminal

xterm-256color