Improve visual distinction of user messages in VSCode chat panel

Problem

In the Claude Code VSCode extension chat panel, user messages and assistant messages have very similar visual styling. This makes it difficult to quickly scan the conversation and locate your own messages, especially in longer exchanges.

Suggestion

Add visual differentiation for user messages — for example:

• A colored background (e.g., subtle blue bubble, similar to iMessage/Slack conventions)
• A distinct border or left accent bar
• Slightly different alignment or indentation

This would significantly improve readability and make it easier to follow the conversation flow.

Context

This is a UX/accessibility concern. When working on complex tasks with long back-and-forth exchanges, being able to quickly spot your own messages matters for context and orientation.

Environment

• VSCode (macOS)
• Claude Code extension