[FEATURE]: Preserve Model Selection Per Chat

[AmrTamer23]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

When I open a chat and select for example Model X and then open another chat with Model Y, the model selected in the first chat becomes Model Y, I think preserving model selection per chat is super helpful for running multiple chats at the same time.

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: Session-persistent model override via Ctrl+M #12669: [FEATURE]: Session-persistent model override via Ctrl+M — requests that model selection persist throughout a session rather than reverting to the agent default
• [Bug] TUI model selection gets overwritten by agent default model #13456: [Bug] TUI model selection gets overwritten by agent default model — reports that manually selected models are overwritten and not persisted per session
• TUI: User selected agent/model is overwritten by server defaults when creating a new session #7948: TUI: User selected agent/model is overwritten by server defaults when creating a new session — similar issue where user model/agent selection is reset

Please review these issues and consider adding your input there if they match your use case.