ruler support (#5758)

# Description of Changes

<img width="266" height="228" alt="image"
src="https://github.com/user-attachments/assets/bcc6ec11-bd9e-4b83-a081-62149dd92f2a"
/>

<img width="882" height="335" alt="image"
src="https://github.com/user-attachments/assets/b86dbf13-6bcf-4b28-81a6-8c405358a58e"
/>

<img width="1050" height="399" alt="image"
src="https://github.com/user-attachments/assets/6a4468ed-d0f9-44ab-978a-c640d490da8b"
/>

on hover
<img width="380" height="196" alt="image"
src="https://github.com/user-attachments/assets/ba3755b3-4823-48dc-b6aa-3a0f9b0517a3"
/>

---

## Checklist

### General

- [ ] 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/devGuide/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/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] 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/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### 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/devGuide/DeveloperGuide.md#6-testing)
for more details.

frontend/public/locales/en-GB/translation.toml

@@ -4273,6 +4273,7 @@ rotateRight = "Rotate Right"
 toggleSidebar = "Toggle Sidebar"
 toggleBookmarks = "Toggle Bookmarks"
 print = "Print PDF"
+ruler = "Ruler / Measure"
 draw = "Draw"
 redact = "Redact"
 exitRedaction = "Exit Redaction Mode"