Model Observers: Audit Changes Without Messy Controllers

Observers let you react to model events like created, updated, deleted.

    This helps for:
    - audit logs
    - cache invalidation
    - notifications
    
    ## Create an observer
    
    ```bash
    php artisan make:observer PostObserver --model=Post
    ```
    
    ## Example: log updates
    
    ```php
    public function updated(Post $post): void {
      AuditLog::create([
        'entity' => 'post',
        'entity_id' => $post->id,
        'action' => 'updated',
        'user_id' => auth()->id(),
      ]);
    }
    ```
    
    ## Register observer
    
    ```php
    Post::observe(PostObserver::class);
    ```
    
    ## Flow
    
    ```mermaid
    flowchart LR
      A[Post Updated] --> B[Observer Triggered]
      B --> C[Audit Log Saved]
    ```
    
    In the next tutorial, we will implement request validation + DTO patterns for cleaner services.