Normalize labor category sort_order + fix increment step to 10

Migration renumbers all categories per company as 10, 20, 30… to
eliminate existing duplicates. Observer now increments by 10 instead
of 1 to leave headroom between positions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Models/Tenant/LaborCategory.php

@@ -35,7 +35,7 @@ class LaborCategory extends Model
                     ->where('company_id', $cat->company_id)
                     ->where('sort_order', '>=', $new)
                     ->where('id', '!=', $cat->id ?? 0)
-                    ->increment('sort_order');
+                    ->increment('sort_order', 10);
             }
         });
     }