[FEATURE] Bring back the user message bubble in the desktop Code tab, or make it a setting

### Preflight Checklist

- [x] I have searched [existing requests](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20label%3Aenhancement) and this feature hasn't been requested yet
- [x] This is a single feature request (not multiple features)

### Problem Statement

Earlier this year the desktop Code tab rendered my prompts as light teal text on a muted blue bubble against the dark background. That treatment is gone in the current builds, and I want to make the case for restoring it, or at minimum offering it as an appearance option.

Screenshot from that period attached. The text is fully legible, and the bubble reads at a glance as mine without competing with Claude's output or tool activity.

Why it matters: in a long agentic session the transcript is mostly tool calls, diffs, and Claude's narration. The thing I most often need to find is my own last instruction: the scope I set, the file I told it not to touch, the constraint I added three turns ago. With the bubble, that was a one-second scroll. Without it, user turns blend into everything else and I end up reading to find them. Several people I work with said the same thing unprompted.

### Proposed Solution

Add a User message style option under Settings > Appearance with the previous teal-on-blue bubble as one choice, or restore it as the dark theme default with the blue toned down if saturation was the concern. The styles existed a few months ago, so this should be a small change.

### Alternative Solutions

Restore the teal-on-blue bubble as the dark theme default, with the blue toned down if saturation was the concern in #48158.

Current workaround: scrolling and reading the transcript, or searching for my own wording with Cmd+F, to find the last instruction I gave.

### Priority

Medium - Would be very helpful

### Feature Category

Configuration and settings

### Use Case Example

1. I'm three hours into a Code tab session on a monorepo, with a dozen tool calls, diffs, and replies since my last instruction.
2. Claude asks whether it should touch a file, and I need to check exactly what scope I set earlier.
3. With the teal-on-blue bubble, my turns stand out from the white text and tool cards as I scroll, and I find the instruction in a second.
4. Without it, I read through the transcript or search for my own wording, which breaks the flow of the review.

### Additional Context

On the objections. #49056 reports dark blue text on black. That is not what shipped on my machine, and it is not what the screenshot shows; the text was light teal and the contrast was high. It looks like a different rendering or theme state, and it deserves its own fix, but it is not a reason to remove the bubble for everyone. #48158 objects to the saturation of the blue against the dark theme. That is a tuning question, not a case against role differentiation.

Meanwhile #42764 and #72427 ask for exactly this: a visually distinct style for user messages so long threads can be scanned. The demand runs both directions, which usually means the answer is a toggle, not a removal.

Happy to test a build.

The issue identifies the desktop Code tab and Settings > Appearance as the relevant entry points; start by locating the transcript message styling and appearance settings. Done means user messages are visually distinguishable again or the requested style can be selected as an appearance option, with the long-session scanning use case verified.

索引モデルが issue の本文から書いたものです。