feat(recipe): Save and Save As for recipes

Custom recipes can be overwritten in place (TopBar SAVE now offers CANCEL /
SAVE AS / SAVE and prefills the current name); bundled recipes stay read-only
and only offer Save As. Adds updateCustomRecipe to storageUtils.

src/utils/storageUtils.ts

@@ -35,6 +35,13 @@ export async function saveCustomRecipe(recipe: Omit<Recipe, 'id' | 'isCustom'>):
   return newRecipe;
 }
 
+// Overwrite an existing custom recipe in place (Save). No-op if the id is gone.
+export async function updateCustomRecipe(id: string, recipe: Omit<Recipe, 'id' | 'isCustom'>): Promise<void> {
+  const custom = await getCustomRecipes();
+  const updated = custom.map((r) => (r.id === id ? { ...r, ...recipe, id, isCustom: true } : r));
+  await AsyncStorage.setItem(CUSTOM_RECIPES_KEY, JSON.stringify(updated));
+}
+
 export async function deleteCustomRecipe(id: string): Promise<void> {
   const custom = await getCustomRecipes();
   const updated = custom.filter(r => r.id !== id);