feat(payments): wallet screen with balances, benefits and storefront

Add the "Кошелёк" section to the settings hub: context-visible chip
balances, active benefits (no-ads term/forever, hints) and a storefront of
chip-priced values and money-priced chip packs. Guests have no wallet; the
Google Play build hides the money purchases behind a RuStore stub; a web
purchase that would draw VK/Telegram chips warns first.

Add the catalog read path the storefront needs — a context-projected
GET /api/v1/user/wallet/catalog (payments service + store, gateway op
wallet.catalog, FBS Catalog/CatalogProduct/CatalogAtom, client decode) —
plus the client leg for the existing wallet.get/buy ops. Value spends reuse
the existing spend path; the chip-pack purchase (money order flow) arrives
with payment intake, so its action is a disabled placeholder for now.

Covered by Go unit (catalog projection) + integration (/wallet/catalog over
Postgres), vitest (formatting, spendable selection, web-spend warning, GP
flag, codec + gateway encode round-trips) and Playwright mock e2e (render,
guest-hidden, GP stub, warning) on Chromium + WebKit.

ui/src/lib/model.ts

@@ -170,6 +170,32 @@ export interface Wallet {
   hints: number;
 }
 
+/** One atom line of a storefront product: the base value type it grants ("chips"/"hints"/
+ *  "noads_days"/"tournament") and how many of it the product carries. */
+export interface CatalogAtom {
+  atomType: string;
+  quantity: number;
+}
+
+/** One storefront product for the caller's context. A "value" is bought with chips (chips is its
+ *  uniform price, money fields zero); a "pack" funds chips with money (moneyAmount is its price in
+ *  the context currency's minor units under moneyCurrency, chips zero). atoms lists what it grants. */
+export interface CatalogProduct {
+  kind: 'value' | 'pack';
+  productId: string;
+  title: string;
+  chips: number;
+  moneyAmount: number;
+  moneyCurrency: string;
+  atoms: CatalogAtom[];
+}
+
+/** The storefront: the products visible and purchasable in the caller's context — the chip-priced
+ *  values and the chip packs priced in the context's payment method. */
+export interface Catalog {
+  products: CatalogProduct[];
+}
+
 export interface Profile {
   userId: string;
   displayName: string;