Move Model Selection into Top Panel

[urmauur]

📋 Summary Relocate the Model Selection control from the Settings panel to the Top Panel / Header Bar for faster access and clearer visibility.

🧠 Proposed Changes

• Add a Model Selector (e.g., dropdown or segmented control) in the top panel, near the chat title or toolbar area.
• Display the currently active model
• Allow quick switching between available models without opening Settings.
• Maintain responsive design — the selector collapses or hides appropriately on smaller screens.

💡 Rationale

• Model switching is a frequent action and should be easily accessible.
• Reduces friction for developers or testers who compare outputs across models.
• Keeps the Settings panel focused on configuration, not runtime controls.

✅ Acceptance Criteria

• Model selector visible in top panel.
• Current model clearly displayed.
• Model switching works identically to current behavior.
• Responsive design verified on desktop and mobile.
• No redundant model controls in Settings.