feat(conversion): add PDF to EPUB/AZW3 conversion support and settings (#5434)

# Description of Changes


This pull request introduces support for converting PDF files to eBook
formats (EPUB and AZW3) in the frontend. It adds new user interface
options for PDF-to-eBook conversion, updates the conversion logic and
parameters, and ensures the new formats are integrated into the
conversion matrix and endpoints. The most important changes are grouped
below:

**PDF to eBook (EPUB/AZW3) Conversion Support**

* Added a new `ConvertToEpubSettings` component that provides UI
controls for PDF-to-eBook options, including chapter detection, target
device selection, and output format.
(`frontend/src/core/components/tools/convert/ConvertToEpubSettings.tsx`)
* Updated `ConvertSettings` to render the new eBook options when
converting from PDF to EPUB or AZW3, and set default values for these
options.
(`frontend/src/core/components/tools/convert/ConvertSettings.tsx`)
* Extended the `ConvertParameters` interface and default parameters to
include `epubOptions` for the new settings.
(`frontend/src/core/hooks/tools/convert/useConvertParameters.ts`)

**Conversion Logic and API Integration**

* Updated the conversion endpoints, endpoint names, and conversion
matrix to support PDF-to-EPUB/AZW3 conversions.
(`frontend/src/core/constants/convertConstants.ts`)
* Modified the conversion operation logic to handle `epubOptions` and
ensure that PDF-to-eBook conversions process each file separately and
send the correct options to the backend.
(`frontend/src/core/hooks/tools/convert/useConvertOperation.ts`)
**Localization and Tool Registry Updates**

* Added localization strings for the new eBook conversion options.
(`frontend/public/locales/en-GB/translation.toml`)
* Registered the new PDF-to-eBook operation in the tool catalog and test
helpers. (`frontend/src/core/data/useTranslatedToolRegistry.tsx`,
`frontend/src/core/tests/helpers/conversionEndpointDiscovery.ts`)



<img width="364" height="995" alt="image"
src="https://github.com/user-attachments/assets/c54c50c0-1b86-4074-aef8-b038c6caeb49"
/>

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- What was changed
- Why the change was made
- Any challenges encountered

Closes #(issue_number)
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---

## 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/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)
- [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/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)

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

### Testing (if applicable)

- [X] 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.

Signed-off-by: Balázs Szücs <[email protected]>
Co-authored-by: Anthony Stirling <[email protected]>

frontend/src/core/constants/convertConstants.ts

@@ -37,6 +37,7 @@ export const CONVERSION_ENDPOINTS = {
   'cbr-pdf': '/api/v1/convert/cbr/pdf',
   'pdf-cbr': '/api/v1/convert/pdf/cbr',
   'ebook-pdf': '/api/v1/convert/ebook/pdf',
+  'pdf-epub': '/api/v1/convert/pdf/epub',
   'pdf-text-editor': '/api/v1/convert/pdf/text-editor',
   'text-editor-pdf': '/api/v1/convert/text-editor/pdf'
 } as const;
@@ -61,6 +62,7 @@ export const ENDPOINT_NAMES = {
   'ebook-pdf': 'ebook-to-pdf',
   'cbr-pdf': 'cbr-to-pdf',
   'pdf-cbr': 'pdf-to-cbr',
+  'pdf-epub': 'pdf-to-epub',
   'pdf-text-editor': 'pdf-to-text-editor',
   'text-editor-pdf': 'text-editor-to-pdf'
 } as const;
@@ -124,13 +126,15 @@ export const TO_FORMAT_OPTIONS = [
   { value: 'webp', label: 'WEBP', group: 'Image' },
   { value: 'html', label: 'HTML', group: 'Web' },
   { value: 'xml', label: 'XML', group: 'Web' },
+  { value: 'epub', label: 'EPUB', group: 'eBook' },
+  { value: 'azw3', label: 'AZW3', group: 'eBook' },
 ];
 
 // Conversion matrix - what each source format can convert to
 export const CONVERSION_MATRIX: Record<string, string[]> = {
   'any': ['pdf'], // Mixed files always convert to PDF
   'image': ['pdf'], // Multiple images always convert to PDF
-  'pdf': ['png', 'jpg', 'gif', 'tiff', 'bmp', 'webp', 'docx', 'odt', 'pptx', 'odp', 'csv', 'txt', 'rtf', 'md', 'html', 'xml', 'pdfa', 'cbz', 'cbr'],
+  'pdf': ['png', 'jpg', 'gif', 'tiff', 'bmp', 'webp', 'docx', 'odt', 'pptx', 'odp', 'csv', 'txt', 'rtf', 'md', 'html', 'xml', 'pdfa', 'cbz', 'cbr', 'epub', 'azw3'],
   'cbz': ['pdf'],
   'docx': ['pdf'], 'doc': ['pdf'], 'odt': ['pdf'],
   'xlsx': ['pdf'], 'xls': ['pdf'], 'ods': ['pdf'],
@@ -159,7 +163,8 @@ export const EXTENSION_TO_ENDPOINT: Record<string, Record<string, string>> = {
     'html': 'pdf-to-html', 'xml': 'pdf-to-xml',
     'pdfa': 'pdf-to-pdfa',
     'cbr': 'pdf-to-cbr',
-    'cbz': 'pdf-to-cbz'
+    'cbz': 'pdf-to-cbz',
+    'epub': 'pdf-to-epub', 'azw3': 'pdf-to-epub'
   },
   'cbz': { 'pdf': 'cbz-to-pdf' },
   'docx': { 'pdf': 'file-to-pdf' }, 'doc': { 'pdf': 'file-to-pdf' }, 'odt': { 'pdf': 'file-to-pdf' },