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/server/handlers_admin_console.go

@@ -102,6 +102,14 @@ func (s *Server) registerConsole(router *gin.Engine) {
 		gm.GET("/banner-settings", s.consoleBannerSettings)
 		gm.POST("/banner-settings", s.consoleUpdateBannerSettings)
 	}
+	if s.payments != nil {
+		gm.GET("/catalog", s.consoleCatalog)
+		gm.POST("/catalog", s.consoleCreateProduct)
+		gm.GET("/catalog/:id", s.consoleCatalogDetail)
+		gm.POST("/catalog/:id", s.consoleUpdateProduct)
+		gm.POST("/catalog/:id/archive", s.consoleArchiveProduct)
+		gm.POST("/catalog/:id/delete", s.consoleDeleteProductAction)
+	}
 }
 
 // consoleDashboard renders the landing page: the top-line counts and the resident