Add visual distinction for user messages in dark mode (background color or sidebar markers)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

In long conversations, it's difficult to locate my own messages when scrolling back through the chat, especially in dark mode where both user and assistant messages blend together visually.
Problem:
Long sessions produce a lot of text from both sides
I use my own messages as landmarks to remember where different stages of work began
In dark mode, there's not enough visual contrast between user and assistant messages
Scrolling through a long conversation to find my inputs takes significant time

Use case:
I work in iterative revision cycles with Claude Code, reviewing builds on my phone and returning with feedback. Being able to quickly jump between my messages would help me track where each review phase started.

Proposed Solution

Suggested solutions (any of these would help):
Allow users to set a custom background color for their own messages
Add a colored sidebar stripe or accent on user messages
Provide a mini-map or message navigator showing where user messages are in the conversation
Add clickable markers/nodes in a sidebar that jump to each user message

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_