feat(slepok): Task 2.11 (backend slice) — ProjectResource serializes applies_from

ProjectResource теперь включает поле `applies_from` (ISO8601 строка | null) в
JSON-ответе. Установлен ProjectService::update() для slepok-sensitive правок
(Task 2.8 dynamic attribute).

UI Vue/composables/Vitest часть откладывается на отдельную сессию — это
backend-only commit для бэкенд-инструмента UI-сообщения.

Spec §4.2.5.

Plan: docs/superpowers/plans/2026-05-26-slepok-routing-protection.md §Task 2.11

Tests: tests/Feature/Http/Resources/ProjectResourceAppliesFromTest.php — 2/2 PASS.

app/app/Http/Resources/ProjectResource.php

@@ -35,6 +35,10 @@ class ProjectResource extends JsonResource
                 $request->routeIs('projects.show'),
                 fn () => $this->getSupplierLinks(),
             ),
+            // Task 2.11 (Spec §4.2.5): dynamic attribute, не БД-поле. Установлен
+            // ProjectService::update() для slepok-sensitive правок. UI показывает
+            // «изменения вступят в силу с DD.MM HH:MM МСК».
+            'applies_from' => $this->applies_from?->toIso8601String(),
         ];
     }
 }

app/tests/Feature/Http/Resources/ProjectResourceAppliesFromTest.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Http\Resources\ProjectResource;
+use App\Models\Project;
+use App\Models\Tenant;
+use Carbon\CarbonImmutable;
+use Illuminate\Foundation\Testing\DatabaseTransactions;
+
+uses(DatabaseTransactions::class);
+
+it('ProjectResource includes applies_from as ISO8601 when set', function (): void {
+    $tenant = Tenant::factory()->create();
+    $project = Project::factory()->for($tenant)->create();
+    $project->applies_from = CarbonImmutable::parse('2026-05-29 21:00:00', 'Europe/Moscow');
+
+    $resource = (new ProjectResource($project))->toArray(request());
+
+    expect($resource)->toHaveKey('applies_from');
+    expect($resource['applies_from'])->toBe('2026-05-29T21:00:00+03:00');
+});
+
+it('ProjectResource applies_from is null when not set', function (): void {
+    $tenant = Tenant::factory()->create();
+    $project = Project::factory()->for($tenant)->create();
+    // applies_from не установлен
+
+    $resource = (new ProjectResource($project))->toArray(request());
+
+    expect($resource)->toHaveKey('applies_from');
+    expect($resource['applies_from'])->toBeNull();
+});