Add Apple Reminders integration for grocery list with local mapping persistence

Introduce a GroceryListManager facade that delegates to either the existing
in-app GroceryList or a new RemindersGroceryStore backed by EventKit. Users
choose the mode in Settings; when Reminders mode is active the Grocery List
tab is hidden. Recipe-to-reminder grouping uses a local mapping file
(reminder_mappings.data) instead of polluting the reminder's notes field,
with automatic pruning when reminders are deleted externally.

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

Nextcloud Cookbook iOS Client/Views/Tabs/GroceryListTabView.swift

@@ -11,7 +11,7 @@ import SwiftUI
 
 
 struct GroceryListTabView: View {
-    @EnvironmentObject var groceryList: GroceryList
+    @EnvironmentObject var groceryList: GroceryListManager
 
     var body: some View {
         NavigationStack {