Fix Chinese localization split page numbering (#3574)

# Description of Changes

Please provide a summary of the changes, including:

- **What was changed**  
Updated the values of `split.desc.6`, `split.desc.7`, and `split.desc.8`
in `src/main/resources/messages_zh_CN.properties` to correct the page
numbers:

- **Why the change was made**  
The previous numbering was inconsistent and would have led to incorrect
split outputs in the Chinese UI. This ensures that users splitting a
document see the correct page ranges.

- **Translation Method**  
The correction of these translation strings was generated and verified
using AI assistance.

Closes #3529

---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] 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/resources/messages_zh_CN.properties

@@ -1075,9 +1075,9 @@ split.desc.2=如选择1,3,7-9将把一个 10 页的文件分割成6个独立的P
 split.desc.3=文档 #1：第 1 页
 split.desc.4=文档 #2：第 2 页和第 3 页
 split.desc.5=文档 #3：第 4 页、第 5 页、第 6 页和第 7 页
-split.desc.6=文档 #4：第 7 页
-split.desc.7=文档 #5：第 8 页
-split.desc.8=文档 #6：第 9 页和第 10 页
+split.desc.6=文档 #4：第 8 页
+split.desc.7=文档 #5：第 9 页
+split.desc.8=文档 #6：第 10 页
 split.splitPages=输入要分割的页面：
 split.submit=拆分