chore(catalog): order the admin catalog list like the public offer

Sales (chip packs) first, ascending by rouble price; then the chip-exchange
values, grouped and price-sorted the same way projectOfferPricing lists them, so
the /catalog console mirrors what a buyer sees. Internal cosmetics only — no
product behaviour change. The value-group order moves to a shared helper
(valueGroup) so the offer and the admin list cannot drift.

backend/internal/payments/offer.go

@@ -109,11 +109,7 @@ func projectOfferPricing(entries []catalogEntry) string {
 	return strings.TrimRight(b.String(), "\n")
 }
 
-// offerValueGroup ranks a chip-priced value into the offer's usage groups, in listing order: hints
-// only (0), no-ads only (1), no-ads + hints (2), then anything carrying the tournament atom (3).
-// Tournament products are not sellable yet (validateProduct forbids an active one), so group 3 is
-// empty today; the rank reserves their place for when the tournament economy lands. A value with no
-// recognised benefit atom sorts after the known groups (defensive — the catalog shape forbids it).
+// offerValueGroup ranks a chip-priced value into the usage groups (see [valueGroup]).
 func offerValueGroup(e catalogEntry) int {
 	hasHints, hasNoAds, hasTournament := false, false, false
 	for _, a := range e.atoms {
@@ -126,6 +122,16 @@ func offerValueGroup(e catalogEntry) int {
 			hasTournament = true
 		}
 	}
+	return valueGroup(hasHints, hasNoAds, hasTournament)
+}
+
+// valueGroup ranks a chip-priced value into the listing groups shared by the public offer and the
+// admin catalog, in listing order: hints only (0), no-ads only (1), no-ads + hints (2), then anything
+// carrying the tournament atom (3). Tournament products are not sellable yet (validateProduct forbids
+// an active one), so group 3 is empty today; the rank reserves their place for when the tournament
+// economy lands. A value with no recognised benefit atom sorts after the known groups (defensive —
+// the catalog shape forbids it).
+func valueGroup(hasHints, hasNoAds, hasTournament bool) int {
 	switch {
 	case hasTournament:
 		return 3