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/ui.ts

@@ -1847,11 +1847,35 @@ export const toolTemplates = {
     </div>
 `,
 
-linearize: () => `
+  linearize: () => `
     <h2 class="text-2xl font-bold text-white mb-4">Linearize PDFs (Fast Web View)</h2>
     <p class="mb-6 text-gray-400">Optimize multiple PDFs for faster loading over the web. Files will be downloaded in a ZIP archive.</p>
     ${createFileInputHTML({ multiple: true, accept: 'application/pdf', showControls: true })} 
     <div id="file-display-area" class="mt-4 space-y-2"></div>
     <button id="process-btn" class="hidden btn-gradient w-full mt-6" disabled>Linearize PDFs & Download ZIP</button> 
   `,
+  'add-attachments': () => `
+    <h2 class="text-2xl font-bold text-white mb-4">Add Attachments to PDF</h2>
+    <p class="mb-6 text-gray-400">First, upload the PDF document you want to add files to.</p>
+    ${createFileInputHTML({ accept: 'application/pdf' })}
+    <div id="file-display-area" class="mt-4 space-y-2"></div>
+
+    <div id="attachment-options" class="hidden mt-8">
+      <h3 class="text-lg font-semibold text-white mb-3">Upload Files to Attach</h3>
+      <p class="mb-4 text-gray-400">Select one or more files to embed within the PDF. You can attach any file type (images, documents, spreadsheets, etc.).</p>
+      
+      <label for="attachment-files-input" class="w-full flex justify-center items-center px-6 py-10 bg-gray-900 text-gray-400 rounded-lg border-2 border-dashed border-gray-600 hover:bg-gray-800 hover:border-gray-500 cursor-pointer transition-colors">
+        <div class="text-center">
+          <svg class="mx-auto h-12 w-12" stroke="currentColor" fill="none" viewBox="0 0 48 48" aria-hidden="true"><path d="M28 8H12a4 4 0 00-4 4v20m32-12v8m0 0v8a4 4 0 01-4 4H12a4 4 0 01-4-4v-4m32-4l-3.172-3.172a4 4 0 00-5.656 0L28 28M8 32l9.172-9.172a4 4 0 015.656 0L28 28m0 0l4 4m4-24h8m-4-4v8" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"></path></svg>
+          <span class="mt-2 block text-sm font-medium">Click to upload files</span>
+          <span class="mt-1 block text-xs">Any file type, multiple files allowed</span>
+        </div>
+        <input id="attachment-files-input" name="attachment-files" type="file" class="sr-only" multiple>
+      </label>
+
+      <div id="attachment-file-list" class="mt-4 space-y-2"></div>
+
+      <button id="process-btn" class="hidden btn-gradient w-full mt-6" disabled>Embed Files & Download</button>
+    </div>
+  `,
 };