Accessibility regressions in v0.17.2: startup splash flash, motion, low-contrast UI, and settings readability

### Prerequisites

- [x] I am running the latest version of ComfyUI
- [ ] I have custom nodes enabled

### What happened?

A user reported multiple accessibility regressions after updating from `0.16.4` to `0.17.2`, severe enough that they plan to revert.

The biggest blockers from the report:

- On frontend load, there is a fake startup animation / splash that flashes full-screen dark before returning to light mode. The reporter uses light mode for accessibility reasons and described the startup flash + motion as photosensitive-triggering and a blocker. They specifically asked for a way to disable this startup splash / animation.
- The settings panel refactor is much harder to parse: controls feel visually detached from their labels, to the point where the reporter has to count rows from separators or shrink the window width significantly just to figure out which control belongs to which label.
- Scrollbars are too thin and too low-contrast against the background, to the point that the reporter can barely tell they are present.
- UI text appears smaller and less visually consistent in places, with weaker visual separation overall and some non-obvious interactive text.
- Extra UI animations are described as a blocker for common accessibility needs. The reporter is asking for a way to disable all of them.
- Nodes 2.0 rendering/performance issues still trigger neurovisual problems badly enough that they cannot assess its accessibility state at all.
- New/changed job popups are also described as more intrusive and no longer avoidable via the prior workaround.

This was reported as happening within the first few minutes of use and causing enough visual strain that the user had to stop for the night.

### Steps to Reproduce

1. Use the frontend in light mode.
2. Update from `0.16.4` to `0.17.2`.
3. Reload/open the frontend.
4. Observe the startup splash / startup animation: it flashes dark full-screen before returning to the configured light theme.
5. Open the settings panel and try to match labels to controls at a normal window width.
6. Try to use the updated UI for a few minutes, including scrolling panels and interacting with queue/progress UI.
7. Observe low-contrast thin scrollbars, weaker visual separation, smaller/harder-to-read text, and motion/animation that is difficult or painful to tolerate.

### How is this affecting you?

Feature doesn't work as expected

### ComfyUI Frontend Version

0.17.2

### Browser

Other

### Console Errors

```javascript
None reported.
```

### Logs

```shell
None reported.
```

### Additional Context

Reporter notes from Discord:

- "Accessibility is getting worse again. I'm gonna have to revert."
- "I do not like the anti-flash bang of the fake startup animation on the frontend load."
- "Need a disable option for this startup splash."
- "The new UI animations is a blocker for common accessibility requirements. Absolutely in need of an option to disable all of these animations."
- "This was all within the first couple minutes of use. My vision hurts too much now, gotta abandon what I had planing to do tonight and rest."

Other points from the report:

- random text appears smaller across the UI
- possibly inconsistent typefaces in adjacent UI elements
- random padding increases reduce information density
- panning performance still feels bad / possibly worse
- Nodes 2.0 disabled may show tearing
- Nodes 2.0 remains inaccessible to this reporter due to rendering issues

Related existing issues that may overlap but do not seem to cover this exact regression report:

- #7445 Accessiblity: Reduced Motion Option
- #6976 Accessibility Issues with new GUI
- #4013 [Feature Request]: Simple animation mode to reduce screen redraws

Screenshots were shared in Discord with the report, but are not attached here.

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-10288-Accessibility-regressions-in-v0-17-2-startup-splash-flash-motion-low-contrast-UI--3286d73d365081ccafe8e3b18513074f) by [Unito](https://www.unito.io)

Start by reproducing the light-mode startup splash, settings-panel label alignment, scrollbar contrast, and motion issues in the frontend, including queue/progress UI and Nodes 2.0. No source files or tests are named, so first locate the relevant frontend entry points and review related issues #7445, #6976, and #4013. Done would require an agreed, testable scope for the reported accessibility regressions and verification that the affected UI is readable and motion can be disabled.

Written by the indexing model from the issue text.