[V2] feat(convert): add PDF/X export option (#5285)

# Description of Changes

This pull request adds support for converting PDF files to PDF/X format
in the frontend, alongside the existing PDF/A conversion. The changes
include UI updates, translation strings, configuration, and processing
logic to enable PDF to PDF/X conversion using the same backend endpoint
as PDF/A, with appropriate user options and warnings.

**PDF/X Conversion Support:**

- Added a new `ConvertToPdfxSettings` component for configuring PDF/X
conversion options, including output format selection and digital
signature warnings.
(`frontend/src/core/components/tools/convert/ConvertToPdfxSettings.tsx`)
- Updated the conversion settings UI to display PDF/X options when
converting from PDF to PDF/X.
(`frontend/src/core/components/tools/convert/ConvertSettings.tsx`)

**Configuration and Processing Logic:**

- Extended conversion constants and parameters to recognize PDF/X as a
target format, map it to the PDF/A backend endpoint, and ensure correct
file naming and processing behavior.
(`frontend/src/core/constants/convertConstants.ts`,
`frontend/src/core/hooks/tools/convert/useConvertOperation.ts`,
`frontend/src/core/hooks/tools/convert/useConvertParameters.ts`)
- Ensured that PDF/X conversions are processed separately per file,
similar to PDF/A.
(`frontend/src/core/hooks/tools/convert/useConvertOperation.ts`)

**UI and Translation Updates:**

- Updated translation strings to include PDF/X options, descriptions,
and warnings. (`frontend/public/locales/en-GB/translation.toml`)

<img width="366" height="998" alt="image"
src="https://github.com/user-attachments/assets/b28fa095-9350-4db2-a0b5-bddcf003fa46"
/>


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Please provide a summary of the changes, including:

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

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---

## 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.

---------

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

frontend/src/core/constants/convertConstants.ts

@@ -110,6 +110,7 @@ export const FROM_FORMAT_OPTIONS = [
 export const TO_FORMAT_OPTIONS = [
   { value: 'pdf', label: 'PDF', group: 'Document' },
   { value: 'pdfa', label: 'PDF/A', group: 'Document' },
+  { value: 'pdfx', label: 'PDF/X', group: 'Document' },
   { value: 'docx', label: 'DOCX', group: 'Document' },
   { value: 'odt', label: 'ODT', group: 'Document' },
   { value: 'cbz', label: 'CBZ', group: 'Archive' },
@@ -136,7 +137,7 @@ export const TO_FORMAT_OPTIONS = [
 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', 'epub', 'azw3'],
+  'pdf': ['png', 'jpg', 'gif', 'tiff', 'bmp', 'webp', 'docx', 'odt', 'pptx', 'odp', 'csv', 'txt', 'rtf', 'md', 'html', 'xml', 'pdfa', 'pdfx', 'cbz', 'cbr', 'epub', 'azw3'],
   'cbz': ['pdf'],
   'docx': ['pdf'], 'doc': ['pdf'], 'odt': ['pdf'],
   'xlsx': ['pdf'], 'xls': ['pdf'], 'ods': ['pdf'],
@@ -164,6 +165,7 @@ export const EXTENSION_TO_ENDPOINT: Record<string, Record<string, string>> = {
     'txt': 'pdf-to-text', 'rtf': 'pdf-to-text', 'md': 'pdf-to-markdown',
     'html': 'pdf-to-html', 'xml': 'pdf-to-xml',
     'pdfa': 'pdf-to-pdfa',
+    'pdfx': 'pdf-to-pdfa',  // PDF/X uses the same endpoint as PDF/A
     'cbr': 'pdf-to-cbr',
     'cbz': 'pdf-to-cbz',
     'epub': 'pdf-to-epub', 'azw3': 'pdf-to-epub'