feat: event dashboard metric cards with stats endpoint (UX-02)

Add GET /events/{event}/stats endpoint returning aggregate counts for
persons (by status, approved without shift), pending identity matches,
and shift fill rates. Frontend metric cards component shows four
actionable KPIs on the event overview tab.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/Http/Controllers/Api/V1/EventController.php

@@ -10,6 +10,7 @@ use App\Http\Requests\Api\V1\UpdateEventRequest;
 use App\Http\Resources\Api\V1\EventResource;
 use App\Models\Event;
 use App\Models\Organisation;
+use App\Models\PersonIdentityMatch;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
 use Illuminate\Http\Resources\Json\AnonymousResourceCollection;
@@ -124,4 +125,57 @@ final class EventController extends Controller
 
         return EventResource::collection($children);
     }
+
+    public function stats(Event $event): JsonResponse
+    {
+        Gate::authorize('view', $event);
+
+        $personCounts = $event->persons()
+            ->selectRaw("
+                COUNT(*) as total,
+                SUM(CASE WHEN status = 'approved' THEN 1 ELSE 0 END) as approved,
+                SUM(CASE WHEN status IN ('pending', 'applied') THEN 1 ELSE 0 END) as pending,
+                SUM(CASE WHEN status = 'rejected' THEN 1 ELSE 0 END) as rejected
+            ")
+            ->first();
+
+        $approvedWithoutShift = $event->persons()
+            ->where('status', 'approved')
+            ->whereDoesntHave('shiftAssignments')
+            ->count();
+
+        $pendingMatches = PersonIdentityMatch::pending()
+            ->whereHas('person', fn ($q) => $q->where('event_id', $event->id))
+            ->count();
+
+        $shifts = $event->festivalSections()
+            ->with(['shifts' => fn ($q) => $q->withCount([
+                'shiftAssignments' => fn ($q) => $q->where('status', 'approved'),
+            ])])
+            ->get()
+            ->flatMap->shifts;
+
+        $shiftsTotal = $shifts->count();
+        $shiftsFilled = $shifts->filter(
+            fn ($s) => $s->shift_assignments_count >= $s->slots_total
+        )->count();
+
+        $total = (int) $personCounts->total;
+        $approved = (int) $personCounts->approved;
+        $pending = (int) $personCounts->pending;
+        $rejected = (int) $personCounts->rejected;
+
+        return response()->json(['data' => [
+            'persons_total' => $total,
+            'persons_approved' => $approved,
+            'persons_pending' => $pending,
+            'persons_rejected' => $rejected,
+            'persons_other' => $total - $approved - $pending - $rejected,
+            'persons_approved_without_shift' => $approvedWithoutShift,
+            'pending_identity_matches' => $pendingMatches,
+            'shifts_total' => $shiftsTotal,
+            'shifts_filled' => $shiftsFilled,
+            'shifts_understaffed' => $shiftsTotal - $shiftsFilled,
+        ]]);
+    }
 }