fix(vk): route the Wallet public-offer link out of the Mini App WebView

The "Public offer" link in the Wallet pointed at the same-origin static
/offer/ page with a plain target=_blank anchor and no click handler. The
Android VK client ignores target=_blank and navigates its own WebView to
the page, stranding the player with no way back to the game (iOS opens a
child browser, so it was unaffected). The existing onExternalLinkClick
router could not help: it escapes only cross-origin links, and /offer/ is
same-origin (a static legal page, not an SPA route).

Add onInAppPageLinkClick, which routes a same-origin, non-SPA page out
through the host escape hatch (Telegram openLink, VK away.php) while
bypassing the cross-origin gate, and attach it to the offer link. Outside
a Mini App host it is a no-op and the anchor's own target=_blank stands.

The "Rules" (About) and ad-banner links already route correctly
(cross-origin + a handler) and are left unchanged.

ui/src/screens/Wallet.svelte

@@ -7,7 +7,7 @@
   import { t, i18n, type MessageKey } from '../lib/i18n/index.svelte';
   import { executionContext, formatAmount, needsWebSpendWarning, spendableChips, type SpendContext } from '../lib/wallet';
   import { isGooglePlayBuild, purchasesHidden } from '../lib/distribution';
-  import { onExternalLinkClick, openExternalUrl } from '../lib/links';
+  import { onExternalLinkClick, onInAppPageLinkClick, openExternalUrl } from '../lib/links';
   import { gatewayOrigin } from '../lib/origin';
   import { vkPlatform, vkShowOrderBox } from '../lib/vk';
   import { telegramOpenInvoice } from '../lib/telegram';
@@ -274,7 +274,7 @@
         {/each}
         {#if packs.length > 0}
           <p class="offer" data-testid="offer">
-            <a href="/offer/" target="_blank" rel="noopener noreferrer">{t('wallet.offer')}</a>
+            <a href="/offer/" target="_blank" rel="noopener noreferrer" onclick={onInAppPageLinkClick}>{t('wallet.offer')}</a>
           </p>
         {:else if !loading}
           <p class="empty">{t('wallet.empty')}</p>