feat(conversion): add SVG to PDF conversion functionality (#5431)

# Description of Changes


This pull request introduces a new SVG to PDF conversion feature,
including both backend and frontend changes. The backend adds a secure,
vector-preserving SVG-to-PDF conversion endpoint with comprehensive SVG
sanitization to prevent XSS and SSRF attacks. The frontend is updated to
route SVG-to-PDF conversions through this new endpoint and to
distinguish SVG from other image formats. Additionally, a new dependency
is added for PDF rendering.

**Backend: SVG to PDF Conversion and Security**

* Adds a new API endpoint and controller (`ConvertSvgToPDF`) for
converting SVG files to PDF, using Batik and PDFBox with vector graphics
preservation and robust error handling.
* Implements SVG sanitization (`SvgSanitizer`) to remove scripts, event
handlers, and dangerous URLs, protecting against XSS and SSRF attacks.
* Introduces a utility (`SvgToPdf`) for rendering SVG to PDF with
timeout protection against resource exhaustion attacks.
* Defines a new request model (`SvgToPdfRequest`) for SVG to PDF
conversion requests.
* Adds the `pdfbox-graphics2d` dependency for vector graphics PDF
rendering.

**Frontend: Routing and Format Handling**

* Updates conversion endpoint constants to add `svg-pdf` and maps SVG
files to use the new `svg-to-pdf` route instead of the generic
image-to-PDF route.
* Removes SVG from the generic image format list and introduces a
dedicated check for SVG format (`isSvgFormat`).
<img width="1133" height="995" alt="image"
src="https://github.com/user-attachments/assets/dec8cf27-ccb9-490d-af76-bff69feb0423"
/>

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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

- [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)
- [X] 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)

- [ ] 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]>

frontend/src/core/utils/convertUtils.ts

@@ -1,4 +1,4 @@
-import { 
+import {
   CONVERSION_ENDPOINTS,
   ENDPOINT_NAMES,
   EXTENSION_TO_ENDPOINT,
@@ -11,15 +11,15 @@ import {
  */
 export const getEndpointName = (fromExtension: string, toExtension: string): string => {
   if (!fromExtension || !toExtension) return '';
-  
+
   let endpointKey = EXTENSION_TO_ENDPOINT[fromExtension]?.[toExtension];
-  
-  // If no explicit mapping exists and we're converting to PDF, 
+
+  // If no explicit mapping exists and we're converting to PDF,
   // fall back to 'any' which uses file-to-pdf endpoint
   if (!endpointKey && toExtension === 'pdf' && fromExtension !== 'any') {
     endpointKey = EXTENSION_TO_ENDPOINT['any']?.[toExtension];
   }
-  
+
   return endpointKey || '';
 };
 
@@ -29,7 +29,7 @@ export const getEndpointName = (fromExtension: string, toExtension: string): str
 export const getEndpointUrl = (fromExtension: string, toExtension: string): string => {
   const endpointName = getEndpointName(fromExtension, toExtension);
   if (!endpointName) return '';
-  
+
   // Find the endpoint URL from CONVERSION_ENDPOINTS using the endpoint name
   for (const [key, endpoint] of Object.entries(CONVERSION_ENDPOINTS)) {
     if (ENDPOINT_NAMES[key as keyof typeof ENDPOINT_NAMES] === endpointName) {
@@ -50,7 +50,11 @@ export const isConversionSupported = (fromExtension: string, toExtension: string
  * Checks if the given extension is an image format
  */
 export const isImageFormat = (extension: string): boolean => {
-  return ['png', 'jpg', 'jpeg', 'gif', 'tiff', 'bmp', 'webp', 'svg'].includes(extension.toLowerCase());
+  return ['png', 'jpg', 'jpeg', 'gif', 'tiff', 'bmp', 'webp'].includes(extension.toLowerCase());
+};
+
+export const isSvgFormat = (extension: string): boolean => {
+  return extension.toLowerCase() === 'svg';
 };
 
 /**
@@ -99,4 +103,4 @@ export const getAvailableToExtensions = (fromExtension: string): Array<{value: s
   return TO_FORMAT_OPTIONS.filter(option =>
     supportedExtensions.includes(option.value)
   );
-};
+};