feat(itinerary): add custom itinerary items with drag-to-reorder

- Add CustomItineraryItem domain model with sortOrder for ordering
- Add CKCustomItineraryItem CloudKit wrapper for persistence
- Create CustomItemService for CRUD operations
- Create CustomItemSubscriptionService for real-time sync
- Add AppDelegate for push notification handling
- Add AddItemSheet for creating/editing items
- Add CustomItemRow with drag handle
- Update TripDetailView with continuous vertical timeline
- Enable drag-to-reorder using .draggable/.dropDestination
- Add inline "Add" buttons after games and travel segments

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

SportsTime/Core/Models/Local/SavedTrip.swift

@@ -101,6 +101,79 @@ final class TripVote {
     }
 }
 
+// MARK: - Local Custom Item (Cache)
+
+@Model
+final class LocalCustomItem {
+    @Attribute(.unique) var id: UUID
+    var tripId: UUID
+    var category: String
+    var title: String
+    var anchorType: String
+    var anchorId: String?
+    var anchorDay: Int
+    var createdAt: Date
+    var modifiedAt: Date
+    var pendingSync: Bool  // True if needs to sync to CloudKit
+
+    init(
+        id: UUID = UUID(),
+        tripId: UUID,
+        category: CustomItineraryItem.ItemCategory,
+        title: String,
+        anchorType: CustomItineraryItem.AnchorType = .startOfDay,
+        anchorId: String? = nil,
+        anchorDay: Int,
+        createdAt: Date = Date(),
+        modifiedAt: Date = Date(),
+        pendingSync: Bool = false
+    ) {
+        self.id = id
+        self.tripId = tripId
+        self.category = category.rawValue
+        self.title = title
+        self.anchorType = anchorType.rawValue
+        self.anchorId = anchorId
+        self.anchorDay = anchorDay
+        self.createdAt = createdAt
+        self.modifiedAt = modifiedAt
+        self.pendingSync = pendingSync
+    }
+
+    var toItem: CustomItineraryItem? {
+        guard let category = CustomItineraryItem.ItemCategory(rawValue: category),
+              let anchorType = CustomItineraryItem.AnchorType(rawValue: anchorType)
+        else { return nil }
+
+        return CustomItineraryItem(
+            id: id,
+            tripId: tripId,
+            category: category,
+            title: title,
+            anchorType: anchorType,
+            anchorId: anchorId,
+            anchorDay: anchorDay,
+            createdAt: createdAt,
+            modifiedAt: modifiedAt
+        )
+    }
+
+    static func from(_ item: CustomItineraryItem, pendingSync: Bool = false) -> LocalCustomItem {
+        LocalCustomItem(
+            id: item.id,
+            tripId: item.tripId,
+            category: item.category,
+            title: item.title,
+            anchorType: item.anchorType,
+            anchorId: item.anchorId,
+            anchorDay: item.anchorDay,
+            createdAt: item.createdAt,
+            modifiedAt: item.modifiedAt,
+            pendingSync: pendingSync
+        )
+    }
+}
+
 // MARK: - User Preferences
 
 @Model