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/Views/MainView.swift

@@ -99,12 +99,12 @@ struct MainView: View {
             await groceryList.load()
             groceryList.configureSyncManager(appState: appState)
             if UserSettings.shared.grocerySyncEnabled {
-                await groceryList.syncManager?.performInitialSync()
+                await groceryList.syncManager?.performSync()
             }
             await mealPlan.load()
             mealPlan.configureSyncManager(appState: appState)
             if UserSettings.shared.mealPlanSyncEnabled {
-                await mealPlan.syncManager?.performInitialSync()
+                await mealPlan.syncManager?.performSync()
             }
             recipeViewModel.presentLoadingIndicator = false
         }