feat(admin): product catalog editor

The /_gm console gains a Catalog editor — the source of truth for products.
Create / edit / archive-unarchive products, their atom composition and per-rail
prices (RUB via direct / VOTE via vk / XTR via telegram / CHIP value), and
hard-delete only a never-transacted product (an order or ledger reference forces
archive-only, backed by the FK RESTRICT). The archived flag reuses the existing
product.active. Activation revalidates the sellable shape — a pack (the chips
atom ⇒ a money price per rail, chips-only) or a value (no chips ⇒ a CHIP price);
a tournament-bearing product is composable but never sellable yet.

Backed by payments AdminCatalog / CreateProduct / UpdateProduct /
SetProductActive / DeleteProduct + a pure validateProduct.

Tests: validateProduct (pack / value / tournament / duplicate / shape); the
console editor end to end (create, edit, archive, delete-if-clean, refuse a
transacted delete).

backend/internal/payments/catalog_admin_test.go

@@ -0,0 +1,47 @@
+package payments
+
+import "testing"
+
+func TestValidateProduct(t *testing.T) {
+	pack := ProductInput{
+		Title:  "100 chips",
+		Atoms:  []AtomLine{{Atom: "chips", Quantity: 100}},
+		Prices: []PriceLine{{Method: "direct", Currency: CurrencyRUB, Amount: 14900}},
+	}
+	value := ProductInput{
+		Title:  "5 hints",
+		Atoms:  []AtomLine{{Atom: "hints", Quantity: 5}},
+		Prices: []PriceLine{{Method: "", Currency: CurrencyChip, Amount: 50}},
+	}
+
+	tests := []struct {
+		name     string
+		in       ProductInput
+		sellable bool
+		wantErr  bool
+	}{
+		{"valid pack", pack, true, false},
+		{"valid value", value, true, false},
+		{"pack with a benefit atom", ProductInput{Title: "x", Atoms: []AtomLine{{"chips", 100}, {"hints", 5}}, Prices: pack.Prices}, true, true},
+		{"pack without money price", ProductInput{Title: "x", Atoms: pack.Atoms, Prices: value.Prices}, true, true},
+		{"value without chip price", ProductInput{Title: "x", Atoms: value.Atoms, Prices: pack.Prices}, true, true},
+		{"tournament sellable is refused", ProductInput{Title: "cup", Atoms: []AtomLine{{"tournament", 1}}, Prices: value.Prices}, true, true},
+		{"tournament draft is allowed", ProductInput{Title: "cup", Atoms: []AtomLine{{"tournament", 1}}}, false, false},
+		{"unknown atom", ProductInput{Title: "x", Atoms: []AtomLine{{"gold", 1}}}, false, true},
+		{"duplicate atom", ProductInput{Title: "x", Atoms: []AtomLine{{"hints", 1}, {"hints", 2}}}, false, true},
+		{"non-positive quantity", ProductInput{Title: "x", Atoms: []AtomLine{{"hints", 0}}}, false, true},
+		{"chip price with a method", ProductInput{Title: "x", Atoms: value.Atoms, Prices: []PriceLine{{Method: "direct", Currency: CurrencyChip, Amount: 50}}}, true, true},
+		{"money price without a method", ProductInput{Title: "x", Atoms: pack.Atoms, Prices: []PriceLine{{Method: "", Currency: CurrencyRUB, Amount: 149}}}, true, true},
+		{"duplicate price", ProductInput{Title: "x", Atoms: pack.Atoms, Prices: []PriceLine{{Method: "direct", Currency: CurrencyRUB, Amount: 1}, {Method: "direct", Currency: CurrencyRUB, Amount: 2}}}, true, true},
+		{"empty title", ProductInput{Title: " ", Atoms: value.Atoms, Prices: value.Prices}, true, true},
+		{"no atoms", ProductInput{Title: "x", Prices: value.Prices}, true, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := validateProduct(tt.in, tt.sellable)
+			if (err != nil) != tt.wantErr {
+				t.Fatalf("validateProduct = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}