Split Opacity slider into 2 separate sliders for second chat

**Is your feature request related to a problem? Please describe.**
I really like my chatboxes to have very little opacity but the second chat box if i turn the opacity to 0 the text nearly disappears
**Describe the solution you'd like**
Would it be possible to split the second chat opacity slider into 2 sliders one for text opacity and one for background opacity of the chat box?

**Describe alternatives you've considered**
None

**Additional context**
None

Look for UI configuration files or classes handling chat box opacity settings, likely in the GUI or rendering modules. Identify where the current single slider is defined and modify to add separate controls for text and background opacity. Test changes in-game to ensure both sliders work independently without breaking existing functionality.

索引モデルが issue の本文から書いたものです。