feat: Jan lets user choose which GPU to run Model on

[dan-jan]

Problem Feature requested by Sabin_Stargem from r/localllama

• I actually think this is a great idea, especially for multi-modal AI
• Niche feature for power users with multi-GPU setups
• UI will need to avoid overcomplicating it for "normie" users

Success Criteria A clear and concise description of what you want to happen.

Additional context Add any other context or screenshots about the feature request here.