fix: improve debounce task cancellation handling

- Add cancelPendingSync() method for explicit cleanup
- Use [weak self] capture to prevent potential retain issues
- Check Task.isCancelled before and after sleep
- Catch CancellationError from Task.sleep for immediate cancellation response
- Extract debounceInterval as constant

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

SportsTime/Core/Services/ItineraryItemService.swift

@@ -16,9 +16,16 @@ actor ItineraryItemService {
     private var debounceTask: Task<Void, Never>?
 
     private let maxRetries = 3
+    private let debounceInterval: Duration = .seconds(1.5)
 
     private init() {}
 
+    /// Cancel any pending debounce task (for cleanup)
+    func cancelPendingSync() {
+        debounceTask?.cancel()
+        debounceTask = nil
+    }
+
     // MARK: - CRUD Operations
 
     /// Fetch all items for a trip
@@ -45,16 +52,25 @@ actor ItineraryItemService {
     func updateItem(_ item: ItineraryItem) async {
         pendingUpdates[item.id] = item
 
-        // Cancel existing debounce
+        // Cancel existing debounce task
         debounceTask?.cancel()
 
-        // Start new debounce
-        debounceTask = Task {
-            try? await Task.sleep(for: .seconds(1.5))
-
+        // Start new debounce task with proper cancellation handling
+        debounceTask = Task { [weak self] in
+            // Check cancellation before sleeping
             guard !Task.isCancelled else { return }
 
-            await flushPendingUpdates()
+            do {
+                try await Task.sleep(for: self?.debounceInterval ?? .seconds(1.5))
+            } catch {
+                // Task was cancelled during sleep
+                return
+            }
+
+            // Check cancellation after sleeping (belt and suspenders)
+            guard !Task.isCancelled else { return }
+
+            await self?.flushPendingUpdates()
         }
     }