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/codec.ts

@@ -40,6 +40,9 @@ import type {
   Profile,
   Wallet,
   WalletSegment,
+  Catalog,
+  CatalogProduct,
+  CatalogAtom,
   ProfileUpdate,
   PushEvent,
   Seat,
@@ -388,6 +391,33 @@ export function decodeWallet(buf: Uint8Array): Wallet {
   };
 }
 
+// decodeCatalog reads the storefront payload: the context-visible products, each a chip-priced
+// value or a chip pack priced in the context's payment method, with its atom composition.
+export function decodeCatalog(buf: Uint8Array): Catalog {
+  const c = fb.Catalog.getRootAsCatalog(new ByteBuffer(buf));
+  const products: CatalogProduct[] = [];
+  for (let i = 0; i < c.productsLength(); i++) {
+    const p = c.products(i);
+    if (!p) continue;
+    const atoms: CatalogAtom[] = [];
+    for (let j = 0; j < p.atomsLength(); j++) {
+      const a = p.atoms(j);
+      if (!a) continue;
+      atoms.push({ atomType: s(a.atomType()), quantity: a.quantity() });
+    }
+    products.push({
+      kind: s(p.kind()) === 'pack' ? 'pack' : 'value',
+      productId: s(p.productId()),
+      title: s(p.title()),
+      chips: p.chips(),
+      moneyAmount: Number(p.moneyAmount()),
+      moneyCurrency: s(p.moneyCurrency()),
+      atoms,
+    });
+  }
+  return { products };
+}
+
 export function decodeProfile(buf: Uint8Array): Profile {
   const p = fb.Profile.getRootAsProfile(new ByteBuffer(buf));
   return {