Add more quality options for GPT Image 2.5, select model for side chat and more!

Added xhigh and max quality options, plus 4K landscape (3840x2160) and portrait (2160x3840) resolutions for GPT Image 2.5. Also reordered resolution and quality options for easier selection.

Side Chat Model Selection: Users can now choose which model powers the side chat "Ask..." feature (highlight text in a chat → select Ask...), either via a new setting or directly from the side chat popup.

Temporary Chat for Agents: Added support for temporary chat when using agents.