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/screens/SettingsHub.svelte

@@ -4,15 +4,17 @@
   import Settings from './Settings.svelte';
   import Profile from './Profile.svelte';
   import Friends from './Friends.svelte';
+  import Wallet from './Wallet.svelte';
   import About from './About.svelte';
   import { app } from '../lib/app.svelte';
   import { offlineMode } from '../lib/offline.svelte';
   import { t, type MessageKey } from '../lib/i18n/index.svelte';
 
   // The Settings hub: a single nav bar + bottom tab bar hosting the Settings / Profile /
-  // Friends / About bodies. Tabs switch in place (no navigation), so the back control
-  // always returns to the lobby. Guests have no social surface, so the Friends tab hides.
-  type SettingsTab = 'settings' | 'profile' | 'friends' | 'about';
+  // Friends / Wallet / About bodies. Tabs switch in place (no navigation), so the back control
+  // always returns to the lobby. Guests have no social surface and no wallet, so the Friends and
+  // Wallet tabs hide for them.
+  type SettingsTab = 'settings' | 'profile' | 'friends' | 'wallet' | 'about';
   let { initialTab = 'settings' }: { initialTab?: SettingsTab } = $props();
 
   const guest = $derived(app.profile?.isGuest ?? true);
@@ -20,21 +22,22 @@
   // the hub is keyed by route in App.svelte, so initialTab is constant for its lifetime.
   // svelte-ignore state_referenced_locally
   let tab = $state<SettingsTab>(initialTab);
-  // A guest who deep-links to the Friends tab falls back to Settings.
+  // A guest who deep-links to the Friends or Wallet tab (durable-only surfaces) falls back to Settings.
   $effect(() => {
-    if (guest && tab === 'friends') tab = 'settings';
+    if (guest && (tab === 'friends' || tab === 'wallet')) tab = 'settings';
   });
   // Offline mode has no network, so the Profile and Friends surfaces (which read/save over the
   // network) are disabled — fall back to Settings if the hub is on one (a deep-link or a live flip).
   // Settings stays reachable: it holds the online/offline toggle.
   $effect(() => {
-    if (offlineMode.active && (tab === 'profile' || tab === 'friends')) tab = 'settings';
+    if (offlineMode.active && (tab === 'profile' || tab === 'friends' || tab === 'wallet')) tab = 'settings';
   });
 
   const titleKey: Record<SettingsTab, MessageKey> = {
     settings: 'settings.title',
     profile: 'profile.title',
     friends: 'friends.title',
+    wallet: 'wallet.title',
     about: 'about.title',
   };
 </script>
@@ -46,6 +49,8 @@
     <Profile />
   {:else if tab === 'friends'}
     <Friends />
+  {:else if tab === 'wallet'}
+    <Wallet />
   {:else}
     <About />
   {/if}
@@ -63,6 +68,11 @@
           <span class="face"><span class="sq" aria-hidden="true">🤝{#if app.notifications > 0}<span class="badge">{app.notifications}</span>{/if}</span><span class="lbl">{t('friends.title')}</span></span>
         </button>
       {/if}
+      {#if !guest}
+        <button class="tab" class:active={tab === 'wallet'} disabled={offlineMode.active} onclick={() => (tab = 'wallet')}>
+          <span class="face"><span class="sq" aria-hidden="true">👛</span><span class="lbl">{t('wallet.tab')}</span></span>
+        </button>
+      {/if}
       <button class="tab" class:active={tab === 'about'} onclick={() => (tab = 'about')}>
         <span class="face"><span class="sq" aria-hidden="true">ℹ️{#if app.feedbackReplyUnread}<span class="badge">1</span>{/if}</span><span class="lbl">{t('about.tab')}</span></span>
       </button>