fix: critical error message visibility bug in dark mode (#30570)

## **Description**

This PR fixes critical error message visibility in dark mode.
Previously, error messages used a hardcoded color value that didn't
respect theme preferences.

The improvement changes the `color` property to `inherit` in the
critical error component, ensuring proper color inheritance from the
parent theme based on the user's prefers-color-scheme setting.

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## **Related issues**

Fixes: #30569

## **Manual testing steps**

1. Open `app/scripts/ui.js`
2. Locate the `initializeUiWithTab` function
3. Throw an error
   ```javascript
   // To test critical error display, uncomment the next line:
   throw new Error('Test Critical Error');
   ```
4. Enable dark mode in your system preferences or via dev tools (see
recording)
5. Verify error message text properly inherits dark theme colors
6. Switch to light mode and verify error message remains visible

## **Screenshots/Recordings**

<!-- If applicable, add screenshots and/or recordings to visualize the
before and after of your change. -->

### **Before**


https://github.com/user-attachments/assets/e2c59c38-f7ab-4755-828e-32f6696b1bbd

### **After**


https://github.com/user-attachments/assets/44fd7f34-792f-47e5-be48-7fb1c051d961

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask
Extension Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I've included tests if applicable
- [x] I've documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I've applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

ui/css/errors.scss

@@ -3,7 +3,7 @@
   border-radius: 4px;
   border-left: var(--color-warning-default) 4px solid;
   background-color: var(--color-warning-muted);
-  color: var(--color-text-default);
+  color: inherit; // Required to inherit color set from prefers-color-scheme
   display: flex;
   padding: 12px 12px 12px 8px;
   gap: 8px;