feat(android): resolve gateway origin on native, skip SW, hide MVP purchases

Make the web SPA behave correctly inside the Capacitor native shell, where the
bundle loads from a local origin:

- New lib/origin.ts gatewayOrigin(): absolute URLs resolve to VITE_GATEWAY_URL on
  native (the finished-game export/share URL in Game.svelte and the Wallet
  site-root link), falling back to the page origin on web. transport.ts already
  resolved via VITE_GATEWAY_URL and is left as-is.
- Skip the PWA service worker on the native channel (the assets are already local;
  a worker would risk serving stale content across store updates).
- Hide the money-purchase UI in the MVP: new distribution.purchasesHidden() folds
  VITE_PAYMENTS_DISABLED and the Google Play flag. The Wallet "buy" tab shows a
  neutral, pointer-free note (wallet.purchasesSoon) for the RuStore MVP and keeps
  the RuStore stub Google-Play-only. A ?nopay mock force mirrors ?gp for the e2e.
- Native env types in vite-env.d.ts.

Client-only, contour-safe: no wire/proto/schema change; web/VK/Telegram unchanged.
Tests: origin + purchasesHidden unit tests, a ?nopay wallet e2e. svelte-check
clean, vitest green, web + native vite build clean.

ui/src/game/Game.svelte

@@ -28,6 +28,7 @@
   import { alphabetLetters, hasAlphabet } from '../lib/alphabet';
   import { hintsLeft, hintGateRemainingMs, hintLockMinutes, HINT_GATE_MS } from '../lib/hints';
   import { downloadUrl, shareOrDownloadGcg, shareUrlAsFile } from '../lib/share';
+  import { gatewayOrigin } from '../lib/origin';
   import { insideVK, vkAndroidWebView, vkCopyText, vkDownloadFile, vkPlatform, vkShowImages } from '../lib/vk';
   import { getCachedGame, setCachedGame, setCachedDraft, type CachedGame } from '../lib/gamecache';
   import { patchLobbyGame } from '../lib/lobbycache';
@@ -1211,7 +1212,7 @@
       const dateLocale = typeof navigator !== 'undefined' ? (navigator.language ?? '') : '';
       const timeZone = Intl.DateTimeFormat().resolvedOptions().timeZone ?? '';
       const { path, filename } = await gateway.exportUrl(id, kind, dateLocale, labels, timeZone);
-      const url = new URL(path, location.origin).href;
+      const url = new URL(path, gatewayOrigin()).href;
       const mime = kind === 'png' ? 'image/png' : 'text/plain';
       if (insideTelegram() && !tgShareSheet && telegramDownloadFile(url, filename)) return;
       if (insideVK()) {