feat(organisation): add dashboard-stats endpoint

GET /organisations/{organisation}/dashboard-stats returns members,
events (with status breakdown + active count), persons, the first five
members sorted by join date, and the five most recent activity log
entries. Business logic lives in OrganisationDashboardService; access
follows OrganisationPolicy@view.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api/app/Http/Resources/Api/V1/OrganisationDashboardStatsResource.php

@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Resources\Api\V1;
+
+use Illuminate\Http\Request;
+use Illuminate\Http\Resources\Json\JsonResource;
+
+/**
+ * @property-read array<string, mixed> $resource
+ */
+final class OrganisationDashboardStatsResource extends JsonResource
+{
+    public function toArray(Request $request): array
+    {
+        return [
+            'members_count' => $this->resource['members_count'],
+            'events_count' => $this->resource['events_count'],
+            'events_by_status' => $this->resource['events_by_status'],
+            'active_events_count' => $this->resource['active_events_count'],
+            'persons_count' => $this->resource['persons_count'],
+            'top_members' => $this->resource['top_members'],
+            'recent_activity' => $this->resource['recent_activity'],
+        ];
+    }
+}