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.

backend/internal/payments/service.go

@@ -54,6 +54,18 @@ func (s *Service) Wallet(ctx context.Context, accountID uuid.UUID, cxt Context,
 	return view, nil
 }
 
+// Catalog returns the storefront for the execution context: every chip-priced value (shown in
+// every context) plus the chip packs priced in the context's payment method. It is read straight
+// from the catalog tables — small and rarely edited, so uncached. An untrusted context has no
+// method and so shows values only; buying is gate-checked on Spend regardless (fail-closed).
+func (s *Service) Catalog(ctx context.Context, cxt Context) (CatalogView, error) {
+	entries, err := s.store.loadCatalog(ctx)
+	if err != nil {
+		return CatalogView{}, err
+	}
+	return projectCatalog(entries, cxt), nil
+}
+
 // AdFree reports whether ads are suppressed for the account in the context: some origin
 // applicable there has an active no-ads term or the forever flag. Fail-closed on an untrusted
 // platform (no origin applies).