[FEATURE]: Theme keys for per-role message text colors and grouped Q&A background in conversation history #20897

Feature hasn't been suggested before.

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Describe the enhancement you want to request

Summary

The current theme schema exposes no way to visually distinguish message types in the conversation history. All messages share the same text/markdownText color. When scrolling back through a long session it is difficult to quickly locate a specific request or a Q&A exchange.

Requested changes

1. Per-role text color keys

Add theme keys to independently color each message role in the history:

• userMessageText -- color of the user's typed requests/prompts
• assistantMessageText -- color of regular assistant responses

2. Grouped Q&A background

When the assistant asks a clarifying question and the user answers, that exchange should be visually grouped. Add theme keys:

• qaGroupBackground -- background color applied to the entire assistant-question + user-answer block
• qaGroupText -- (optional) text color override within that block

This makes it trivial to scroll back through history and instantly locate where a request was made or where a Q&A exchange happened.

Example theme usage

{
  "theme": {
    "userMessageText": "#A8D8A8",
    "assistantMessageText": "#D8D8D8",
    "qaGroupBackground": "#2A2A40",
    "qaGroupText": "#E8E8FF"
  }
}

Motivation

In long sessions with many tool calls and responses, it becomes hard to navigate the history. Distinct colors per role and a highlighted background for Q&A exchanges would make the history scannable at a glance.

The key distinction from a simple "two-color" approach is the grouped background for Q&A blocks, which is what gives you the fast-scroll landmark you're looking for.