Add customizable colors for system messages (particularly context compacting notifications)

Is your feature request related to a problem? Please describe.
The "context left before conversation compacting" message can be easily missed during conversations because it uses the same styling as regular text. This makes it difficult to notice when context is being lost, which is important information for understanding conversation flow.

Describe the solution you'd like
Add configuration options to customize the color/styling of system messages, particularly:

• Context compacting notifications
• Other important system messages

This could be implemented as:

1. Additional options in the /config command for message styling
2. CSS class-based styling that users can customize
3. Predefined color schemes for different message types

Describe alternatives you've considered

• Using different text formatting (bold, italic) for system messages
• Adding prefixes or symbols to make messages more noticeable
• Sound notifications for important system messages

Additional context
This would improve accessibility and user awareness of important system events during conversations.