feat(api): enrich TimeSlotResource with shift statistics

Add shifts_count, total_slots, filled_slots, and sections_count computed
fields to TimeSlotResource. Update TimeSlotController to eager-load shifts
with assignment counts for aggregate calculations. Includes test verifying
only approved assignments count towards filled_slots.

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

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

@@ -20,11 +20,24 @@ final class TimeSlotController extends Controller
     {
         Gate::authorize('viewAny', [TimeSlot::class, $event]);
 
-        $timeSlots = $event->timeSlots()->orderBy('date')->orderBy('start_time')->get();
+        $timeSlots = $event->timeSlots()
+            ->withCount('shifts')
+            ->with(['shifts' => fn ($q) => $q->withCount([
+                'shiftAssignments as assignments_count' => fn ($q) => $q->where('status', 'approved'),
+            ])])
+            ->orderBy('date')
+            ->orderBy('start_time')
+            ->get();
 
         if ($event->isSubEvent() && request()->boolean('include_parent') && $event->parent_event_id) {
             $parentTimeSlots = TimeSlot::where('event_id', $event->parent_event_id)
-                ->with('event')
+                ->withCount('shifts')
+                ->with([
+                    'event',
+                    'shifts' => fn ($q) => $q->withCount([
+                        'shiftAssignments as assignments_count' => fn ($q) => $q->where('status', 'approved'),
+                    ]),
+                ])
                 ->orderBy('date')
                 ->orderBy('start_time')
                 ->get();

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

@@ -23,6 +23,21 @@ final class TimeSlotResource extends JsonResource
             'duration_hours' => $this->duration_hours,
             'source' => $this->resource->getAttribute('source'),
             'event_name' => $this->whenLoaded('event', fn () => $this->event->name),
+            'shifts_count' => $this->whenCounted('shifts'),
+            // Aggregates computed from eager-loaded shifts with assignment counts.
+            // For events with >200 shifts, consider replacing with a raw aggregate query.
+            'total_slots' => $this->when(
+                $this->relationLoaded('shifts'),
+                fn () => (int) $this->shifts->sum('slots_total'),
+            ),
+            'filled_slots' => $this->when(
+                $this->relationLoaded('shifts'),
+                fn () => (int) $this->shifts->sum(fn ($shift) => $shift->assignments_count ?? 0),
+            ),
+            'sections_count' => $this->when(
+                $this->relationLoaded('shifts'),
+                fn () => $this->shifts->pluck('festival_section_id')->unique()->count(),
+            ),
             'created_at' => $this->created_at->toIso8601String(),
         ];
     }