feat(api): Implement API Resource Standard compliance

- Create BaseResource with formatDate() and formatDecimal() utilities
- Create 11 API Resource classes for all models
- Update all 6 controllers to return wrapped responses via wrapResource()
- Update frontend API client with unwrapResponse() helper
- Update all 63+ backend tests to expect 'data' wrapper
- Regenerate Scribe API documentation

BREAKING CHANGE: All API responses now wrap data in 'data' key per architecture spec.

Backend Tests: 70 passed, 5 failed (unrelated to data wrapper)
Frontend Unit: 10 passed
E2E Tests: 102 passed, 20 skipped
API Docs: Generated successfully

Refs: openspec/changes/api-resource-standard

backend/app/Http/Resources/HolidayResource.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace App\Http\Resources;
+
+class HolidayResource extends BaseResource
+{
+    public function toArray($request): array
+    {
+        return [
+            'id' => $this->id,
+            'date' => $this->date?->toDateString(),
+            'name' => $this->name,
+            'description' => $this->description,
+        ];
+    }
+}