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/server/server_test.go

@@ -167,7 +167,12 @@ func newTestSearch(t *testing.T) *recipes.SearchSettingsService {
 // with its own unstarted job runner and a grounder that finds nothing.
 func newTestDinners(t *testing.T) *dinners.Service {
 	t.Helper()
-	st := newTestStore(t)
+	return newTestDinnersOn(t, newTestStore(t))
+}
+
+// newTestDinnersOn is newTestDinners over st.
+func newTestDinnersOn(t *testing.T, st *store.Store) *dinners.Service {
+	t.Helper()
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
 	runner, err := jobs.NewRunner(st, logger, 1)
 	if err != nil {