Restructure frontend code to allow for extensions (#4721)

# Description of Changes
Move frontend code into `core` folder and add infrastructure for
`proprietary` folder to include premium, non-OSS features

frontend/src/core/utils/fileResponseUtils.ts

@@ -0,0 +1,45 @@
+/**
+ * Generic utility functions for handling file responses from API endpoints
+ */
+
+/**
+ * Extracts filename from Content-Disposition header
+ * @param contentDisposition - Content-Disposition header value
+ * @returns Filename if found, null otherwise
+ */
+export const getFilenameFromHeaders = (contentDisposition: string = ''): string | null => {
+  const match = contentDisposition.match(/filename[^;=\n]*=((['"]).*?\2|[^;\n]*)/);
+  if (match && match[1]) {
+    const filename = match[1].replace(/['"]/g, '');
+
+    // Decode URL-encoded characters (e.g., %20 -> space)
+    try {
+      return decodeURIComponent(filename);
+    } catch {
+      // If decoding fails, return the original filename
+      return filename;
+    }
+  }
+  return null;
+};
+
+/**
+ * Creates a File object from API response using the filename from headers
+ * @param responseData - The response data (blob/arraybuffer/string)
+ * @param headers - Response headers object
+ * @param fallbackFilename - Filename to use if none provided in headers
+ * @returns File object
+ */
+export const createFileFromApiResponse = (
+  responseData: any,
+  headers: any,
+  fallbackFilename: string
+): File => {
+  const contentType = headers?.['content-type'] || 'application/octet-stream';
+  const contentDisposition = headers?.['content-disposition'] || '';
+
+  const filename = getFilenameFromHeaders(contentDisposition) || fallbackFilename;
+  const blob = new Blob([responseData], { type: contentType });
+
+  return new File([blob], filename, { type: contentType });
+};