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

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)
- [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/components/tools/convert/ConvertFromSvgSettings.tsx

@@ -0,0 +1,41 @@
+import { Stack, Text, Switch } from "@mantine/core";
+import { useTranslation } from "react-i18next";
+import { ConvertParameters } from "@app/hooks/tools/convert/useConvertParameters";
+
+interface ConvertFromSvgSettingsProps {
+  parameters: ConvertParameters;
+  onParameterChange: <K extends keyof ConvertParameters>(key: K, value: ConvertParameters[K]) => void;
+  disabled?: boolean;
+}
+
+const ConvertFromSvgSettings = ({
+  parameters,
+  onParameterChange,
+  disabled = false
+}: ConvertFromSvgSettingsProps) => {
+  const { t } = useTranslation();
+
+  return (
+    <Stack gap="sm" data-testid="svg-pdf-options-section">
+      <Text size="sm" fw={500}>{t("convert.svgPdfOptions", "SVG to PDF Options")}:</Text>
+      
+      <Switch
+        data-testid="combine-svgs-switch"
+        label={t("convert.combineSvgs", "Combine SVGs into single PDF")}
+        description={t("convert.combineSvgsDescription", "Combine all SVG files into one PDF with multiple pages, or create separate PDFs for each SVG")}
+        checked={parameters.imageOptions.combineImages}
+        onChange={(event) => onParameterChange('imageOptions', {
+          ...parameters.imageOptions,
+          combineImages: event.currentTarget.checked
+        })}
+        disabled={disabled}
+      />
+
+      <Text size="xs" c="dimmed" mt="xs">
+        {t("convert.svgVectorNote", "SVG files are rendered as vector graphics for crisp output at any resolution. Dimensions from the SVG determine the PDF page size.")}
+      </Text>
+    </Stack>
+  );
+};
+
+export default ConvertFromSvgSettings;

frontend/src/core/components/tools/convert/ConvertSettings.tsx

@@ -20,6 +20,7 @@ import ConvertToPdfaSettings from "@app/components/tools/convert/ConvertToPdfaSe
 import ConvertFromCbrSettings from "@app/components/tools/convert/ConvertFromCbrSettings";
 import ConvertToCbrSettings from "@app/components/tools/convert/ConvertToCbrSettings";
 import ConvertFromEbookSettings from "@app/components/tools/convert/ConvertFromEbookSettings";
+import ConvertFromSvgSettings from "@app/components/tools/convert/ConvertFromSvgSettings";
 import ConvertToEpubSettings from "@app/components/tools/convert/ConvertToEpubSettings";
 import { ConvertParameters } from "@app/hooks/tools/convert/useConvertParameters";
 import {
@@ -331,6 +332,18 @@ const ConvertSettings = ({
         </>
       ) : null}
 
+      {/* SVG to PDF options */}
+      {parameters.fromExtension === 'svg' && parameters.toExtension === 'pdf' && (
+        <>
+          <Divider />
+          <ConvertFromSvgSettings
+            parameters={parameters}
+            onParameterChange={onParameterChange}
+            disabled={disabled}
+          />
+        </>
+      )}
+
       {/* Web to PDF options */}
       {((isWebFormat(parameters.fromExtension) && parameters.toExtension === 'pdf') ||
        (parameters.isSmartDetection && parameters.smartDetectionType === 'web')) ? (