feat: Add required and filled slots to Shift entity and update ShiftDetailsPage for capacity display

apps/mobile/packages/domain/lib/src/entities/shifts/shift.dart

@@ -24,6 +24,8 @@ class Shift extends Equatable {
   final double? longitude;
   final String? status;
   final int? durationDays; // For multi-day shifts
+  final int? requiredSlots;
+  final int? filledSlots;
 
   const Shift({
     required this.id,
@@ -49,6 +51,8 @@ class Shift extends Equatable {
     this.longitude,
     this.status,
     this.durationDays,
+    this.requiredSlots,
+    this.filledSlots,
   });
 
   @override
@@ -76,6 +80,8 @@ class Shift extends Equatable {
         longitude,
         status,
         durationDays,
+        requiredSlots,
+        filledSlots,
       ];
 }