Overlay PDF tool (#4620)

# Description of Changes

- Added the OverlayPDF tool

---

## 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)

### 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/src/components/tooltips/useOverlayPdfsTips.ts

@@ -0,0 +1,56 @@
+import { useTranslation } from 'react-i18next';
+import { TooltipContent } from '../../types/tips';
+
+export const useOverlayPdfsTips = (): TooltipContent => {
+  const { t } = useTranslation();
+
+  return {
+    header: {
+      title: t('overlay-pdfs.tooltip.header.title', 'Overlay PDFs Overview')
+    },
+    tips: [
+      {
+        title: t('overlay-pdfs.tooltip.description.title', 'Description'),
+        description: t(
+          'overlay-pdfs.tooltip.description.text',
+          'Combine a base PDF with one or more overlay PDFs. Overlays can be applied page-by-page in different modes and placed in the foreground or background.'
+        )
+      },
+      {
+        title: t('overlay-pdfs.tooltip.mode.title', 'Overlay Mode'),
+        description: t(
+          'overlay-pdfs.tooltip.mode.text',
+          'Choose how to distribute overlay pages across the base PDF pages.'
+        ),
+        bullets: [
+          t('overlay-pdfs.tooltip.mode.sequential', 'Sequential Overlay: Use pages from the first overlay PDF until it ends, then move to the next.'),
+          t('overlay-pdfs.tooltip.mode.interleaved', 'Interleaved Overlay: Take one page from each overlay in turn.'),
+          t('overlay-pdfs.tooltip.mode.fixedRepeat', 'Fixed Repeat Overlay: Take a set number of pages from each overlay before moving to the next. Use Counts to set the numbers.')
+        ]
+      },
+      {
+        title: t('overlay-pdfs.tooltip.position.title', 'Overlay Position'),
+        description: t(
+          'overlay-pdfs.tooltip.position.text',
+          'Foreground places the overlay on top of the page. Background places it behind.'
+        )
+      },
+      {
+        title: t('overlay-pdfs.tooltip.overlayFiles.title', 'Overlay Files'),
+        description: t(
+          'overlay-pdfs.tooltip.overlayFiles.text',
+          'Select one or more PDFs to overlay on the base. The order of these files affects how pages are applied in Sequential and Fixed Repeat modes.'
+        )
+      },
+      {
+        title: t('overlay-pdfs.tooltip.counts.title', 'Counts (Fixed Repeat only)'),
+        description: t(
+          'overlay-pdfs.tooltip.counts.text',
+          'Provide a positive number for each overlay file showing how many pages to take before moving to the next. Required when mode is Fixed Repeat.'
+        )
+      }
+    ]
+  };
+};
+
+