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/social.spec.ts

@@ -238,7 +238,10 @@ test('profile edit disables Save and flags an invalid display name', async ({ pa
   await expect(save).toBeEnabled();
 });
 
-test('link account: a taken email opens the irreversible merge confirmation', async ({ page }) => {
+// Account linking is hidden in Profile.svelte while we target provider sign-in (the anonymous
+// /app/ guest who upgrades by linking comes later). The flow is kept wired; re-enable these two
+// specs together with the `.emailbox` section.
+test.skip('link account: a taken email opens the irreversible merge confirmation', async ({ page }) => {
   await loginLobby(page);
   await openProfile(page);
 
@@ -258,7 +261,7 @@ test('link account: a taken email opens the irreversible merge confirmation', as
   await expect(page.getByText('Merge accounts?')).toBeHidden();
 });
 
-test('link account: the Telegram web sign-in control is offered in a browser', async ({ page }) => {
+test.skip('link account: the Telegram web sign-in control is offered in a browser', async ({ page }) => {
   await loginLobby(page);
   await openProfile(page);
   await expect(page.getByRole('button', { name: 'Link Telegram' })).toBeVisible();