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/client.ts

@@ -34,6 +34,8 @@ import type {
   Tile,
   Variant,
   WordCheckResult,
+  Wallet,
+  Catalog,
 } from './model';
 
 /** GatewayError carries a stable code (the gateway result_code, or an edge code). */
@@ -135,6 +137,17 @@ export interface GatewayClient {
   /** feedbackUnread reports whether an operator reply awaits delivery (the badge). */
   feedbackUnread(): Promise<boolean>;
 
+  // --- wallet ---
+  /** wallet returns the caller's chip segments and active benefits, visible in their current
+   *  trusted execution context (view-only when the platform is untrusted or VK-iOS frozen). */
+  wallet(): Promise<Wallet>;
+  /** catalog returns the storefront for the caller's context: chip-priced values and the chip
+   *  packs priced in the context's payment method. */
+  catalog(): Promise<Catalog>;
+  /** walletBuy spends chips on a chip-priced value and returns the updated wallet. Gate-checked
+   *  server-side: an untrusted/frozen context or an insufficient balance is refused. */
+  walletBuy(productId: string): Promise<Wallet>;
+
   // --- friends ---
   friendsList(): Promise<AccountRef[]>;
   friendsIncoming(): Promise<AccountRef[]>;