Do not derive model context from prompt and output token limits

[juanrgon]

Describe the bug

The model details display can overstate total context if it derives context by adding max_prompt_tokens and max_output_tokens. These are independent maxima and their sum may exceed max_context_window_tokens.

Affected version

1.0.81

Steps to reproduce the behavior

1. Return synthetic model metadata with max_prompt_tokens: 100000, max_output_tokens: 20000, and max_context_window_tokens: 100000.
2. Open the CLI model details display.
3. Check whether it reports 120,000 tokens instead of the declared 100,000-token context window.

Expected behavior

Display max_context_window_tokens as the total context window. Treat prompt and output limits as independent maxima rather than values whose sum defines context.

Additional context

The Copilot SDK/runtime preserves the independent context value, so this appears limited to CLI presentation.