fix: Change User model fillable field from 'fullname' to 'name'

This commit fixes an inconsistency between:
- User model (using 'fullname')
- Migration template (using 'name')
- Schema JSON example (using 'name')

This ensures consistent field naming across the framework.

Author: screenfluent

app/models/User.php

@@ -9,7 +9,7 @@ class User extends Model
      * @var array
      */
     protected $fillable = [
-        'fullname', 'email', 'password',
+        'name', 'email', 'password',
     ];
 
     /**