feat(pdf-tools): add attachments feature to embed files in PDFs

Implement new functionality to allow embedding attachments into PDF documents. The feature includes:
- UI for selecting PDF and files to attach
- Logic to embed files while preserving metadata
- Display of attached files with size information
- Download of modified PDF with embedded files

src/js/config/pdf-tools.ts

@@ -38,6 +38,7 @@ export const singlePdfLoadTools = [
   'form-filler',
   'posterize',
   'remove-blank-pages',
+  'add-attachments',
 ];
 
 export const simpleTools = [