fix(ui): retry Mini App launch on backend failure; hide account linking

Inside Telegram, a failed initData authentication (e.g. the backend down
during a deploy) dropped the user onto the web login screen — the /app/
experience, which has no place inside the Mini App. bootstrap now retries the
launch a few times in silence and then renders a dedicated boot-error screen
with a Retry button (new BootError.svelte, app.bootError), never falling back
to the web sign-in. A blocked account is still terminal and goes straight to
the blocked screen.

The profile "Link an account" section (email + Telegram link) is hidden while
sign-in is provider-only; the anonymous /app/ guest whose upgrade path this is
comes later. The flow is kept wired (`hidden` on .emailbox) and its two e2e
specs are skipped, both to be re-enabled together.

Adds i18n boot.* copy (en/ru), a mock authTelegram failure hook plus an e2e
covering the retry screen, and bakes both behaviours into FUNCTIONAL(.md/_ru).

ui/e2e/telegram.spec.ts

@@ -83,6 +83,30 @@ test('tg-fullscreen header keeps a constant native-nav gap as the font scales',
   expect(large.overflows).toBe(false);
 });
 
+test('inside Telegram, a failed launch shows the retry screen, not the web login', async ({ page }) => {
+  // initData carrying the mock's "bootfail" sentinel makes authTelegram reject, simulating a
+  // backend outage during launch (e.g. a deploy rolling). The Mini App must surface its own
+  // boot-error/retry screen and never fall back to the web (guest/email) login.
+  await page.addInitScript(() => {
+    Object.assign(window, {
+      Telegram: {
+        WebApp: {
+          initData: 'query_id=bootfail&user=%7B%22id%22%3A1%7D&auth_date=1&hash=deadbeef',
+          initDataUnsafe: {},
+          ready() {},
+          expand() {},
+        },
+      },
+    });
+  });
+  await page.goto('/');
+
+  // After the silent retries, the boot-error screen with its Retry button shows…
+  await expect(page.getByRole('button', { name: 'Retry' })).toBeVisible();
+  // …and the web login (guest) is never shown inside Telegram.
+  await expect(page.getByRole('button', { name: /guest/i })).toHaveCount(0);
+});
+
 test('outside Telegram, the /telegram/ entry redirects to the site root', async ({ page }) => {
   await page.goto('/telegram/');