fix(export): per-platform polish from the on-device review

- TG iOS: the OS share sheet with the fetched file (WKWebView has
  navigator.share — the долгоживущий debug-overlay Share path proves
  it). The chooser stays the app modal on this one platform: a native
  popup callback cannot supply the user activation the sheet needs.
  TG Android/desktop keep the native popup + downloadFile (verified
  perfect, untouched).
- VK mobile: the PNG now rides VKWebAppDownloadFile like the GCG — the
  owner-verified path that lands in VK's native share flow; the
  ShowImages viewer is dropped (its preview offered save only, no
  share).
- VK desktop iframe: both formats are plain anchor downloads (it is an
  ordinary browser; the viewer/bridge path made no sense there).

ui/e2e/export.spec.ts

@@ -70,6 +70,7 @@ test('inside Telegram the chooser is the native popup and delivery the native do
         WebApp: {
           initData: 'query_id=test&user=%7B%22id%22%3A1%7D&auth_date=1&hash=deadbeef',
           initDataUnsafe: {},
+          platform: 'android',
           ready() {},
           expand() {},
           showPopup(params: { buttons?: { id?: string; type?: string }[] }, cb: (id: string) => void) {
@@ -142,6 +143,60 @@ test('a mobile browser gets the OS share sheet with the fetched file', async ({
   expect(shared.type).toBe('image/png');
 });
 
+test('Telegram on iOS keeps the app chooser and opens the OS share sheet', async ({ page }) => {
+  // TG iOS: WKWebView has navigator.share, and the sheet is the preferred delivery — but
+  // it needs the user activation a native-popup callback cannot provide, so the chooser
+  // stays the app modal on this one platform.
+  await page.addInitScript(() => {
+    const shared: { name: string; type: string }[] = [];
+    Object.defineProperty(navigator, 'canShare', { value: () => true, configurable: true });
+    Object.defineProperty(navigator, 'share', {
+      value: async (data: { files?: File[] }) => {
+        for (const f of data.files ?? []) shared.push({ name: f.name, type: f.type });
+      },
+      configurable: true,
+    });
+    (window as unknown as { __shared: typeof shared }).__shared = shared;
+    Object.assign(window, {
+      Telegram: {
+        WebApp: {
+          initData: 'query_id=test&user=%7B%22id%22%3A1%7D&auth_date=1&hash=deadbeef',
+          initDataUnsafe: {},
+          platform: 'ios',
+          ready() {},
+          expand() {},
+          showPopup() {
+            (window as unknown as { __popupCalled?: boolean }).__popupCalled = true;
+          },
+          downloadFile() {
+            (window as unknown as { __downloadCalled?: boolean }).__downloadCalled = true;
+          },
+        },
+      },
+    });
+  });
+  await routeDl(page);
+  await page.goto('/');
+  await expect(page.getByText('Your turn')).toBeVisible();
+  await page.getByRole('button', { name: /Rick/ }).click();
+  await expect(page.locator('[data-cell]').first()).toBeVisible();
+  await page.locator('.scoreboard').click();
+  await page.getByRole('button', { name: 'Export game' }).click();
+
+  // The app modal opened (both formats) — the native popup was not used…
+  await expect(page.getByRole('button', { name: 'Image (PNG)' })).toBeVisible();
+  await page.getByRole('button', { name: 'Image (PNG)' }).click();
+  // …and the artifact went to the OS share sheet, not TG's download dialog.
+  await expect
+    .poll(() => page.evaluate(() => (window as unknown as { __shared: unknown[] }).__shared))
+    .toHaveLength(1);
+  const flags = await page.evaluate(() => {
+    const w = window as unknown as { __popupCalled?: boolean; __downloadCalled?: boolean };
+    return { popup: !!w.__popupCalled, download: !!w.__downloadCalled };
+  });
+  expect(flags).toEqual({ popup: false, download: false });
+});
+
 test('a legacy Telegram client (no downloadFile) hides the image and copies the GCG', async ({ page }) => {
   await page.addInitScript(() => {
     // Headless engines deny the real clipboard; a permissive stub keeps the legacy