feat(ui): add auto-refresh after upload and inline file preview

- Auto-refresh files table after successful uploads using custom event
- Add inline preview support for PDFs, images, and text files
- Set Content-Disposition header to inline for preview endpoint
- Add download button as secondary action in file details view

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

frontend/static/js/upload.js

@@ -195,6 +195,12 @@ function updateOverallStatus(statusMessage) {
   
   if (completed === total) {
     statusMessage.textContent = `All uploads completed (${completed}/${total})`;
+    
+    // Trigger a custom event when all uploads are complete
+    const allUploadsComplete = new CustomEvent('allUploadsComplete', {
+      detail: { total: total, completed: completed }
+    });
+    window.dispatchEvent(allUploadsComplete);
   } else {
     statusMessage.textContent = `Uploading files (${completed}/${total})`;
   }