Chat settings (model, mode) are shared globally instead of per-session

[touch2be]

Description

Chat settings like the AI model and mode (e.g. Build/Plan) are shared across all sessions instead of being stored per session. Changing settings in one session unexpectedly affects all other sessions.

Observed Behavior

1. Open a chat session and select a model (e.g. GPT-5.4) and mode (e.g. Build)
2. Switch to a different session — it shows the same model and mode settings
3. Change the model or mode in the second session
4. Switch back to the first session — the settings there have also changed

This means all sessions always share the same configuration, making it impossible to have different settings per session.

Expected Behavior

• Each chat session should have its own independent settings (model, mode, etc.)
• Changing settings in one session should not affect other sessions
• When switching sessions, the previously selected settings for that session should be restored

Environment

• OpenGUI Desktop Interface
• OS: Linux

[akemmanuel]

Closing as duplicate of #22.