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.

gateway/internal/transcode/transcode.go

@@ -53,6 +53,7 @@ const (
 	MsgFeedbackGet          = "feedback.get"
 	MsgFeedbackUnread       = "feedback.unread"
 	MsgWalletGet            = "wallet.get"
+	MsgWalletCatalog        = "wallet.catalog"
 	MsgWalletBuy            = "wallet.buy"
 )
 
@@ -108,6 +109,7 @@ func NewRegistry(backend *backendclient.Client, tg TelegramValidator, opts ...Op
 	r.ops[MsgAuthEmailConfirmLink] = Op{Handler: authEmailConfirmLinkHandler(backend)}
 	r.ops[MsgProfileGet] = Op{Handler: profileHandler(backend), Auth: true}
 	r.ops[MsgWalletGet] = Op{Handler: walletHandler(backend), Auth: true}
+	r.ops[MsgWalletCatalog] = Op{Handler: walletCatalogHandler(backend), Auth: true}
 	r.ops[MsgWalletBuy] = Op{Handler: walletBuyHandler(backend), Auth: true}
 	r.ops[MsgBlockStatus] = Op{Handler: blockStatusHandler(backend), Auth: true}
 	r.ops[MsgGameSubmitPlay] = Op{Handler: submitPlayHandler(backend), Auth: true}
@@ -308,6 +310,16 @@ func walletHandler(backend *backendclient.Client) Handler {
 	}
 }
 
+func walletCatalogHandler(backend *backendclient.Client) Handler {
+	return func(ctx context.Context, req Request) ([]byte, error) {
+		cat, err := backend.Catalog(ctx, req.UserID)
+		if err != nil {
+			return nil, err
+		}
+		return encodeCatalog(cat), nil
+	}
+}
+
 func walletBuyHandler(backend *backendclient.Client) Handler {
 	return func(ctx context.Context, req Request) ([]byte, error) {
 		in := fb.GetRootAsWalletBuyRequest(req.Payload, 0)