Enforce Locale.US for Consistent Decimal Formatting in Byte-Size Output (#3562)

# Description of Changes

Please provide a summary of the changes, including:

- **What was changed**  
  - Added `import java.util.Locale;`  
- Updated the `String.format` call in `humanReadableByteCount` to use
`Locale.US`

- **Why the change was made**  
By default, `String.format` uses the JVM’s default locale, which in some
environments (e.g., Germany) formats decimals with a comma. Tests
expected a dot (`.`) as the decimal separator (e.g., `"1.0 KB"`), so we
force `Locale.US` to ensure consistent output across all locales.


---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#6-testing)
for more details.

src/main/java/stirling/software/SPDF/controller/web/UploadLimitService.java

@@ -1,5 +1,6 @@
 package stirling.software.SPDF.controller.web;
 
+import java.util.Locale;
 import java.util.regex.Pattern;
 
 import org.springframework.beans.factory.annotation.Autowired;
@@ -52,6 +53,6 @@ public class UploadLimitService {
         if (bytes < 1024) return bytes + " B";
         int exp = (int) (Math.log(bytes) / Math.log(1024));
         String pre = "KMGTPE".charAt(exp - 1) + "B";
-        return String.format("%.1f %s", bytes / Math.pow(1024, exp), pre);
+        return String.format(Locale.US, "%.1f %s", bytes / Math.pow(1024, exp), pre);
     }
 }