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.test.ts

@@ -15,6 +15,7 @@ import {
   decodeOutgoingList,
   decodeProfile,
   decodeWallet,
+  decodeCatalog,
   encodeWalletBuy,
   decodeSession,
   decodeFeedbackState,
@@ -72,6 +73,54 @@ describe('codec', () => {
     expect(w.hints).toBe(5);
   });
 
+  it('round-trips the catalog view (value + pack)', () => {
+    const b = new Builder(256);
+
+    // a chip-priced value with one atom
+    const vKind = b.createString('value');
+    const vId = b.createString('val-1');
+    const vTitle = b.createString('50 hints');
+    const aType = b.createString('hints');
+    fb.CatalogAtom.startCatalogAtom(b);
+    fb.CatalogAtom.addAtomType(b, aType);
+    fb.CatalogAtom.addQuantity(b, 50);
+    const atom = fb.CatalogAtom.endCatalogAtom(b);
+    const vAtoms = fb.CatalogProduct.createAtomsVector(b, [atom]);
+    fb.CatalogProduct.startCatalogProduct(b);
+    fb.CatalogProduct.addKind(b, vKind);
+    fb.CatalogProduct.addProductId(b, vId);
+    fb.CatalogProduct.addTitle(b, vTitle);
+    fb.CatalogProduct.addChips(b, 100);
+    fb.CatalogProduct.addMoneyAmount(b, BigInt(0));
+    fb.CatalogProduct.addAtoms(b, vAtoms);
+    const value = fb.CatalogProduct.endCatalogProduct(b);
+
+    // a RUB-priced chip pack (no atoms exercised)
+    const pKind = b.createString('pack');
+    const pId = b.createString('pack-1');
+    const pTitle = b.createString('100 chips');
+    const pCur = b.createString('RUB');
+    fb.CatalogProduct.startCatalogProduct(b);
+    fb.CatalogProduct.addKind(b, pKind);
+    fb.CatalogProduct.addProductId(b, pId);
+    fb.CatalogProduct.addTitle(b, pTitle);
+    fb.CatalogProduct.addChips(b, 0);
+    fb.CatalogProduct.addMoneyAmount(b, BigInt(14900));
+    fb.CatalogProduct.addMoneyCurrency(b, pCur);
+    const pack = fb.CatalogProduct.endCatalogProduct(b);
+
+    const prods = fb.Catalog.createProductsVector(b, [value, pack]);
+    fb.Catalog.startCatalog(b);
+    fb.Catalog.addProducts(b, prods);
+    b.finish(fb.Catalog.endCatalog(b));
+
+    const c = decodeCatalog(b.asUint8Array());
+    expect(c.products).toEqual([
+      { kind: 'value', productId: 'val-1', title: '50 hints', chips: 100, moneyAmount: 0, moneyCurrency: '', atoms: [{ atomType: 'hints', quantity: 50 }] },
+      { kind: 'pack', productId: 'pack-1', title: '100 chips', chips: 0, moneyAmount: 14900, moneyCurrency: 'RUB', atoms: [] },
+    ]);
+  });
+
   it('round-trips the export-url request and response', () => {
     const req = fb.ExportUrlRequest.getRootAsExportUrlRequest(
       new ByteBuffer(