refactor: massive codebase stabilization, strict TS, UI/UX overhaul, and central logging

client/src/utils/errorHandlers.ts

@@ -0,0 +1,46 @@
+/**
+ * Type guard to check if a value is an API error response
+ */
+export function isApiError(error: unknown): error is { response?: { status?: number; data?: { message?: string | string[] } } } {
+  return (
+    typeof error === 'object' &&
+    error !== null &&
+    'response' in error &&
+    typeof (error as { response?: unknown }).response === 'object' &&
+    (error as { response?: unknown }).response !== null
+  );
+}
+
+/**
+ * Extract error message from API error response
+ */
+export function getApiErrorMessage(error: unknown, defaultMessage: string = 'Произошла ошибка'): string {
+  if (isApiError(error)) {
+    const data = error.response?.data;
+    const message = data?.message;
+    
+    if (Array.isArray(message)) {
+      return message.join('; ');
+    }
+    
+    if (typeof message === 'string') {
+      return message;
+    }
+  }
+  
+  if (error instanceof Error) {
+    return error.message;
+  }
+  
+  return defaultMessage;
+}
+
+/**
+ * Get HTTP status code from error response
+ */
+export function getApiErrorStatus(error: unknown): number | undefined {
+  if (isApiError(error)) {
+    return error.response?.status;
+  }
+  return undefined;
+}