Keep dinner names frozen in Supply archive posts

Freezing a Supply run now records each group's dinner name in
shopping_groups.frozen_dinner_name, in the same transaction as the
freeze. A frozen list and its Supply archive post read that name, so
renaming a dinner after its week is frozen no longer rewrites the
archive; a current list still shows its dinners' names live.
Migration 0018 adds the column and fills it for lists frozen before it.

Task: 22f80eb6-cdee-4377-80ea-9b28f15a866f

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/db/querier.go

@@ -107,6 +107,9 @@ type Querier interface {
 	// Records a pending or running batch as done or failed; a batch already
 	// finished is left as it is (0 rows).
 	FinishSuggestionBatch(ctx context.Context, arg FinishSuggestionBatchParams) (int64, error)
+	// Keeps the name each dinner of list list_id has now as its group's
+	// frozen_dinner_name, as the list is frozen into the Supply archive.
+	FreezeShoppingGroupNames(ctx context.Context, listID string) error
 	// Freezes list id into the Supply archive at frozen_at, unless it is
 	// frozen already.
 	FreezeShoppingList(ctx context.Context, arg FreezeShoppingListParams) (int64, error)
@@ -228,7 +231,8 @@ type Querier interface {
 	ListRecentPassedNames(ctx context.Context, limit int64) ([]string, error)
 	ListRecipeIngredients(ctx context.Context, recipeID string) ([]RecipeIngredient, error)
 	ListRecipeSteps(ctx context.Context, recipeID string) ([]RecipeStep, error)
-	// The groups of list list_id with their dinner's name, in list order.
+	// The groups of list list_id with their dinner's name now, in list order.
+	// A group of a frozen list shows its frozen_dinner_name instead.
 	ListShoppingGroupDinners(ctx context.Context, listID string) ([]ListShoppingGroupDinnersRow, error)
 	// The groups of list list_id, in list order.
 	ListShoppingGroups(ctx context.Context, listID string) ([]ShoppingGroup, error)