feat(vk): show a launch diagnostic on a direct /vk/ open instead of a guest

Opening the dedicated /vk/ entry directly in an ordinary browser (no signed VK
launch) fell through to the web flow and silently started a throwaway guest,
which is wrong for a VK-only entry. Mirror the existing /telegram/ launch-error
behaviour: render a compact, shareable, privacy-safe diagnostic screen instead.

- Boot: a new branch `onVKPath() && !insideVK()` sets app.launchError and stops
  the fall-through, the VK counterpart of the /telegram/ diagnostic guard.
- Diagnostic (passive, no VK Bridge round-trip): reads the URL launch-parameter
  NAMES (never the `sign` value — auth material), whether the URL was signed,
  `vk_platform`, the iframe/referrer context, plus the shared client-environment
  lines. VK signs the launch URL at load, so — unlike Telegram's initData — the
  parameters never arrive late; hence the VK screen offers Share only, no Retry.
- Generalise the screen: TelegramLaunchError.svelte -> LaunchError.svelte, which
  renders a neutral pre-formatted report and a per-platform title, with Retry
  gated on a `retry` flag (Telegram true, VK false). app.launchError is now a
  neutral LaunchDiag { platform, report, retry }.
- New lib/launchdiag.ts holds the shared pieces both platforms reuse: the
  LaunchDiag shape, the client-environment lines, and the query field-NAME
  reader (moved out of telegram.ts so VK does not duplicate them).

Tests: pure vkDiagLines units, incl. a guard that the `sign` value never leaks
into the report. i18n: launch.errorTitleVk (en/ru). Docs: FUNCTIONAL (+ru) user
story and ARCHITECTURE entry-path note.

docs/ARCHITECTURE.md

@@ -1369,7 +1369,9 @@ Single public origin, path-routed. The Vite build has two entries: a lightweight
 `/app/` (web), `/telegram/` (the Telegram Mini App; on that path without sign-in data
 — no `initData` — the client renders a compact, shareable launch-diagnostic screen instead
 of redirecting away) and `/vk/` (the VK Mini App; the client reads the signed `vk_*` launch
-parameters from the URL and the gateway verifies them in-process — §12); a stray hit on the
+parameters from the URL and the gateway verifies them in-process — §12; on that path without a
+signed launch the client renders the same shareable launch-diagnostic screen rather than starting
+a throwaway guest); a stray hit on the
 gateway's `/` 308-redirects to `/app/`. The **landing** ships in its own static container: the
 `landing` target of `gateway/Dockerfile` (caddy:2-alpine + the same Vite build,
 `deploy/landing/Caddyfile`) serves it at `/`, so stray public traffic is absorbed by

docs/FUNCTIONAL.md

@@ -72,7 +72,10 @@ A **VK Mini App** launch works the same way: it authenticates from VK's signed l
 `vk_language` and its display name from the VK profile (read on the client, since VK does not put
 the name in the signed launch). While the theme preference is "auto" the app follows the VK
 client's light/dark scheme, and the layout clears the VK mobile home bar. The same quiet-retry
-"couldn't load" screen applies inside VK.
+"couldn't load" screen applies inside VK. Opening a Mini App link directly in an ordinary browser —
+the `/vk/` entry with no signed VK launch, or `/telegram/` with no Telegram sign-in data — shows a
+compact, shareable diagnostic screen instead of proceeding (as a throwaway guest on VK, or by
+redirecting away on Telegram), so a player who ends up there wrongly can screenshot it for us.
 **Email** sign-in (web) mails a branded six-digit confirmation code — localized
 (en/ru), no images — to the address; entering it signs the player in. A new address
 is provisioned on the first request but only becomes a durable account once the code

docs/FUNCTIONAL_ru.md

@@ -77,7 +77,10 @@ launch-параметрам VK (их проверяет gateway), и при пе
 так как VK не кладёт имя в подписанный запуск). Пока тема в режиме «авто», приложение следует
 светлой/тёмной схеме VK-клиента, а раскладка обходит нижнюю home-bar VK на мобильных. Тот же экран
 тихого повтора «не удалось
-загрузить» действует и внутри VK.
+загрузить» действует и внутри VK. Если открыть ссылку на мини-приложение прямо в обычном браузере —
+вход `/vk/` без подписанного запуска VK или `/telegram/` без данных входа Telegram — показывается
+компактный экран диагностики, которым можно поделиться, вместо того чтобы продолжить (гостем-однодневкой
+на VK или редиректом прочь на Telegram), — чтобы игрок, случайно попавший туда, прислал нам скриншот.
 **Email**-вход (в вебе) отправляет на адрес брендированный шестизначный код подтверждения —
 локализованный (ru/en), без картинок; после ввода игрок входит. Новый адрес заводится при первом
 запросе, но становится постоянным аккаунтом только после подтверждения кода — так брошенная,