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.d.ts

@@ -0,0 +1,20 @@
+declare const coherentpdf: typeof import('../../src/types/coherentpdf.global').coherentpdf;
+
+interface AddAttachmentsMessage {
+  command: 'add-attachments';
+  pdfBuffer: ArrayBuffer;
+  attachmentBuffers: ArrayBuffer[];
+  attachmentNames: string[];
+}
+
+interface AddAttachmentsSuccessResponse {
+  status: 'success';
+  modifiedPDF: ArrayBuffer;
+}
+
+interface AddAttachmentsErrorResponse {
+  status: 'error';
+  message: string;
+}
+
+type AddAttachmentsResponse = AddAttachmentsSuccessResponse | AddAttachmentsErrorResponse;