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/adminconsole/templates/layout.gohtml

@@ -21,6 +21,7 @@
     <a href="/_gm/throttled"{{if eq .ActiveNav "throttled"}} class="active"{{end}}>Throttled</a>
     <a href="/_gm/reasons"{{if eq .ActiveNav "reasons"}} class="active"{{end}}>Reasons</a>
     <a href="/_gm/banners"{{if eq .ActiveNav "banners"}} class="active"{{end}}>Banners</a>
+    <a href="/_gm/catalog"{{if eq .ActiveNav "catalog"}} class="active"{{end}}>Catalog</a>
     <a href="/_gm/dictionary"{{if eq .ActiveNav "dictionary"}} class="active"{{end}}>Dictionary</a>
     <a href="/_gm/broadcast"{{if eq .ActiveNav "broadcast"}} class="active"{{end}}>Broadcast</a>
     <a href="/_gm/grafana/">Grafana ↗</a>