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/Localizable.xcstrings

@@ -2023,6 +2023,9 @@
           }
         }
       }
+    },
+    "Grocery list state is synced via your Nextcloud server by storing it alongside recipe data." : {
+
     },
     "Grocery list storage" : {
       "localizations" : {
@@ -4319,6 +4322,9 @@
           }
         }
       }
+    },
+    "Sync grocery list across devices" : {
+
     },
     "Thank you for downloading" : {
       "localizations" : {