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/toolErrorHandler.ts

@@ -0,0 +1,33 @@
+/**
+ * Standardized error handling utilities for tool operations
+ */
+
+/**
+ * Default error extractor that follows the standard pattern
+ */
+export const extractErrorMessage = (error: any): string => {
+  if (error.response?.data && typeof error.response.data === 'string') {
+    return error.response.data;
+  }
+  if (error.message) {
+    return error.message;
+  }
+  return 'There was an error processing your request.';
+};
+
+/**
+ * Creates a standardized error handler for tool operations
+ * @param fallbackMessage - Message to show when no specific error can be extracted
+ * @returns Error handler function that follows the standard pattern
+ */
+export const createStandardErrorHandler = (fallbackMessage: string) => {
+  return (error: any): string => {
+    if (error.response?.data && typeof error.response.data === 'string') {
+      return error.response.data;
+    }
+    if (error.message) {
+      return error.message;
+    }
+    return fallbackMessage;
+  };
+};