feat: Implement defensive point constraints and validation tests

app/Http/Controllers/PredefinedMutationController.php

@@ -37,7 +37,7 @@ class PredefinedMutationController extends Controller
         $request->validate([
             'name' => ['required', 'string', 'max:255'],
             'description' => ['nullable', 'string'],
-            'amount' => ['required', 'integer'],
+            'amount' => ['required', 'integer', 'not_in:0', 'min:-1000', 'max:1000'],
         ]);
 
         $ledger->predefinedMutations()->create($request->all());
@@ -69,7 +69,7 @@ class PredefinedMutationController extends Controller
         $request->validate([
             'name' => ['required', 'string', 'max:255'],
             'description' => ['nullable', 'string'],
-            'amount' => ['required', 'integer'],
+            'amount' => ['required', 'integer', 'not_in:0', 'min:-1000', 'max:1000'],
         ]);
 
         $predefinedMutation->update($request->all());

app/Http/Requests/StoreMutationRequest.php

@@ -25,7 +25,7 @@ class StoreMutationRequest extends FormRequest
     public function rules(): array
     {
         return [
-            'amount' => ['required', 'integer'],
+            'amount' => ['required', 'integer', 'not_in:0', 'min:-1000', 'max:1000'],
             'description' => ['required', 'string'],
             'type' => ['nullable', 'string'],
             'status' => ['nullable', 'string'],