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>

migrations/queries/shopping.sql

@@ -60,7 +60,8 @@ DELETE FROM shopping_items
 WHERE id = ?;
 
 -- name: ListShoppingGroupDinners :many
--- 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.
 SELECT sqlc.embed(shopping_groups), dinners.name AS dinner_name
 FROM shopping_groups
 JOIN dinners ON dinners.id = shopping_groups.dinner_id
@@ -117,6 +118,13 @@ UPDATE shopping_lists
 SET status = 'archived', frozen_at = ?, updated_at = ?
 WHERE id = ? AND frozen_at IS NULL;
 
+-- name: FreezeShoppingGroupNames :exec
+-- 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.
+UPDATE shopping_groups
+SET frozen_dinner_name = (SELECT dinners.name FROM dinners WHERE dinners.id = shopping_groups.dinner_id)
+WHERE list_id = ?;
+
 -- name: ListShoppingListsThrough :many
 -- The Supply runs of the weeks starting on or before week_start, newest
 -- week first.