Fix meal plan not populating on first login and add pull-to-refresh sync

Rewrite MealPlanSyncManager.performSync() (renamed from performInitialSync) to
discover _mealPlanAssignment metadata from all server recipes, not just locally-
known ones. On first sync all recipes are checked; on subsequent syncs only
recipes modified since lastMealPlanSyncDate are fetched (max 5 concurrent).

Trigger meal plan sync from pull-to-refresh on both the recipe and meal plan
tabs, and from the "Refresh all" toolbar button.

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

Nextcloud Cookbook iOS Client/Data/UserSettings.swift

@@ -175,6 +175,12 @@ class UserSettings: ObservableObject {
         }
     }
 
+    @Published var lastMealPlanSyncDate: Date? {
+        didSet {
+            UserDefaults.standard.set(lastMealPlanSyncDate, forKey: "lastMealPlanSyncDate")
+        }
+    }
+
     init() {
         self.username = UserDefaults.standard.object(forKey: "username") as? String ?? ""
         self.token = UserDefaults.standard.object(forKey: "token") as? String ?? ""
@@ -203,6 +209,7 @@ class UserSettings: ObservableObject {
         self.categorySortAscending = UserDefaults.standard.object(forKey: "categorySortAscending") as? Bool ?? true
         self.recipeSortMode = UserDefaults.standard.object(forKey: "recipeSortMode") as? String ?? RecipeSortMode.recentlyAdded.rawValue
         self.recipeSortAscending = UserDefaults.standard.object(forKey: "recipeSortAscending") as? Bool ?? true
+        self.lastMealPlanSyncDate = UserDefaults.standard.object(forKey: "lastMealPlanSyncDate") as? Date
 
         if authString == "" {
             if token != "" && username != "" {