Add cross-device grocery list sync via Nextcloud Cookbook API

Store a _groceryState JSON field on each recipe to track which
ingredients have been added, completed, or removed. Uses per-item
last-writer-wins conflict resolution with ISO 8601 timestamps.
Debounced push (2s) avoids excessive API calls; pull reconciles
on recipe open and app launch. Includes a settings toggle to
enable/disable sync.

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

Nextcloud Cookbook iOS Client/Data/UserSettings.swift

@@ -132,6 +132,12 @@ class UserSettings: ObservableObject {
             UserDefaults.standard.set(remindersListIdentifier, forKey: "remindersListIdentifier")
         }
     }
+
+    @Published var grocerySyncEnabled: Bool {
+        didSet {
+            UserDefaults.standard.set(grocerySyncEnabled, forKey: "grocerySyncEnabled")
+        }
+    }
     
     init() {
         self.username = UserDefaults.standard.object(forKey: "username") as? String ?? ""
@@ -154,6 +160,7 @@ class UserSettings: ObservableObject {
         self.decimalNumberSeparator = UserDefaults.standard.object(forKey: "decimalNumberSeparator") as? String ?? "."
         self.groceryListMode = UserDefaults.standard.object(forKey: "groceryListMode") as? String ?? GroceryListMode.inApp.rawValue
         self.remindersListIdentifier = UserDefaults.standard.object(forKey: "remindersListIdentifier") as? String ?? ""
+        self.grocerySyncEnabled = UserDefaults.standard.object(forKey: "grocerySyncEnabled") as? Bool ?? true
         
         if authString == "" {
             if token != "" && username != "" {