Fix meal plan removal ignored on first attempt after app launch

Guard reconcileFromServer() with a syncStartTime so that entries
modified locally during an active performSync() cycle are never
overwritten by stale server data. This prevents the race condition
where a user removes a meal plan entry while Phase 2 of sync is
still iterating server recipes.

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

Nextcloud Cookbook iOS Client/Data/MealPlanSyncManager.swift

@@ -65,6 +65,9 @@ class MealPlanSyncManager {
     func performSync() async {
         guard let appState, let mealPlanManager else { return }
 
+        mealPlanManager.syncStartTime = MealPlanDate.now()
+        defer { mealPlanManager.syncStartTime = nil }
+
         // Phase 1: Push locally-known meal plan state
         let localRecipeIds = Array(Set(
             mealPlanManager.entriesByDate.values.flatMap { $0 }.map(\.recipeId)