Consistent API Errors: Exceptions and Response Format

APIs should return predictable errors so frontend and mobile clients can handle them correctly.

    A common professional format:
    
    ```json
    {
      "error": {
        "code": "OUT_OF_STOCK",
        "message": "This item is no longer available."
      }
    }
    ```
    
    ## Create a custom exception
    
    ```php
    class OutOfStockException extends Exception {
      public function render() {
        return response()->json([
          'error' => [
            'code' => 'OUT_OF_STOCK',
            'message' => $this->getMessage(),
          ],
        ], 409);
      }
    }
    ```
    
    ## Use it
    
    ```php
    if ($product->stock <= 0) {
      throw new OutOfStockException('This item is no longer available.');
    }
    ```
    
    ## Graph: centralized error handling
    
    ```mermaid
    flowchart LR
      A[Service/Controller throws] --> B[Exception Handler]
      B --> C[Standard JSON Error]
      C --> D[Client]
    ```
    
    In the next tutorial, we will implement API request validation using form requests for APIs.