Error handling utility

[ishaan000]

Adds a TypeScript utility for standardized API error handling that:

• Handles success responses (2xx) with flash messages
• Captures validation errors and info messages (4xx, 5xx)
• Provides type-safe access to response data and error details
• Includes status code tracking
• Throws structured ApiError for consistent error handling

Example usage:

try {
  const response = await fetch('/api/endpoint');
  const data = await handleApiError<ResponseType>(response);
  // Success case
  console.log(data.flash?.success);
} catch (error) {
  if (error instanceof ApiError) {
    console.log(error.statusCode); // 400
    console.log(error.flash?.info); // ["Password must be at least 8 characters long."]
  }
}