feat(attachments,security): migrate attachment processing to web worker and update CORS policy

- Add web worker for PDF attachment processing to improve performance and prevent UI blocking
- Create add-attachments.worker.js with TypeScript definitions for type safety
- Implement worker message handling with success and error responses
- Update nginx.conf to use Cross-Origin-Resource-Policy instead of Cross-Origin-Embedder-Policy for better cross-origin resource sharing
- Refactor add-attachments.ts to use worker-based processing with transferable objects
- Update main.ts to add home logo click handler for navigation
- Improve error handling with worker error event listener
- Add validation checks for PDF file availability before processing attachments

public/workers/add-attachments.worker.js

@@ -0,0 +1,69 @@
+self.importScripts('/coherentpdf.browser.min.js');
+
+function addAttachmentsToPDFInWorker(pdfBuffer, attachmentBuffers, attachmentNames) {
+  try {
+    const uint8Array = new Uint8Array(pdfBuffer);
+    
+    let pdf;
+    try {
+      pdf = coherentpdf.fromMemory(uint8Array, '');
+    } catch (error) {
+      self.postMessage({
+        status: 'error',
+        message: `Failed to load PDF. Error: ${error.message || error}`
+      });
+      return;
+    }
+
+    // Add each attachment to the PDF
+    for (let i = 0; i < attachmentBuffers.length; i++) {
+      try {
+        const attachmentData = new Uint8Array(attachmentBuffers[i]);
+        const attachmentName = attachmentNames[i];
+        
+        // Attach file at document level (page 0)
+        coherentpdf.attachFileFromMemory(attachmentData, attachmentName, pdf);
+      } catch (error) {
+        console.warn(`Failed to attach file ${attachmentNames[i]}:`, error);
+        self.postMessage({
+          status: 'error',
+          message: `Failed to attach file ${attachmentNames[i]}: ${error.message || error}`
+        });
+        coherentpdf.deletePdf(pdf);
+        return;
+      }
+    }
+    
+    // Save the modified PDF
+    const modifiedBytes = coherentpdf.toMemory(pdf, false, false);
+    coherentpdf.deletePdf(pdf);
+
+    const buffer = modifiedBytes.buffer.slice(
+      modifiedBytes.byteOffset, 
+      modifiedBytes.byteOffset + modifiedBytes.byteLength
+    );
+
+    self.postMessage({
+      status: 'success',
+      modifiedPDF: buffer
+    }, [buffer]);
+    
+  } catch (error) {
+    self.postMessage({
+      status: 'error',
+      message: error instanceof Error
+        ? error.message
+        : 'Unknown error occurred while adding attachments.'
+    });
+  }
+}
+
+self.onmessage = (e) => {
+  if (e.data.command === 'add-attachments') {
+    addAttachmentsToPDFInWorker(
+      e.data.pdfBuffer, 
+      e.data.attachmentBuffers, 
+      e.data.attachmentNames
+    );
+  }
+};