feat(pwa): installable web app + landing web entry

Make the web SPA an installable PWA and surface it to users:

- manifest.webmanifest + an install-only service worker + 192/512/maskable
  icons (ui/public); PWA head tags in index.html; the .webmanifest MIME type
  registered in the gateway (the distroless image has no /etc/mime.types).
- Platform-adaptive install CTA (components/InstallApp.svelte + lib/pwa):
  one-tap on Chromium, manual Add-to-Home-Screen instructions on iOS Safari,
  hidden elsewhere / once installed / inside a Mini App. Shown under the
  logged-out login card and at the bottom of Settings.
- The landing gains a third entry linking /app/ (the brand tile), with a
  caption under all three (Telegram / VK / Веб-версия).

The service worker is navigation-only (network-first, cached-shell fallback);
hashed assets and the Connect stream are untouched. It exists to satisfy
Chromium's installability requirement and is the single growth point for a
future opt-in offline mode.

Tests: pwa.ts unit tests; a webui probe (manifest/sw.js content-type + the
SPA-fallback-to-HTML trap); e2e for the one-tap CTA, the iOS instructions
modal and the landing web entry. Docs: ARCHITECTURE §13, FUNCTIONAL (+ru),
gateway README.

docs/ARCHITECTURE.md

@@ -1233,7 +1233,14 @@ origin, so the test contour canonicalises to production instead of being indexed
 separate site; the SPA shell is `noindex`, and the landing always boots in Russian (no
 browser-language detection — crawlers render with arbitrary languages). The favicon set,
 `og-image.png` and `robots.txt` ship unhashed from `ui/public/` (generated by
-`assets/icons/`, same tile design as the VK loader). Hash-named `/assets/*` are served
+`assets/icons/`, same tile design as the VK loader). On the web (`/app/`) the SPA is an installable **PWA**:
+`manifest.webmanifest` and an install-only **service worker** (`sw.js`) ship unhashed from
+`ui/public/`, and the client registers the worker **web-only** — never inside a Mini App or the
+mock build. The worker intercepts only top-level navigations (network-first with a cached-shell
+fallback), leaving `/assets/*` and the Connect stream untouched; it exists to satisfy Chromium's
+installability requirement (a registered SW, needed for install on Android) and is the single
+growth point for a future opt-in offline mode. The gateway registers the `.webmanifest` MIME type
+in-process (the distroless image has no `/etc/mime.types`). Hash-named `/assets/*` are served
 `immutable` (a relaunch is a cache hit, not a re-download); the HTML shells are
 `no-cache` so a new deploy is picked up — both containers apply the same caching. An
 in-compose **caddy** is the contour's edge: it owns a single `/_gm` Basic-Auth and

docs/FUNCTIONAL.md

@@ -21,7 +21,8 @@ Settings also pick the board's bonus-label style (beginner / classic / none). A
 costs nothing when the rack has no legal move. The word-check accepts only the
 variant's alphabet, remembers answers within the session and rate-limits repeats.
 A public **landing page** at the site root introduces the game, switches language and
-theme, and links to the Telegram game channel and the VK Mini App; the game itself runs at
+theme, and links to the Telegram game channel, the VK Mini App and the **web version**
+(`/app/`) — each under a caption (Telegram / VK / Веб-версия); the game itself runs at
 `/app/` (web), `/telegram/` (the Telegram Mini App) and `/vk/` (the VK Mini App). The landing's theme is ephemeral
 (it follows the system scheme, not the saved preference); its language choice is saved. The
 landing always opens in **Russian** — the browser language is never auto-detected (crawlers
@@ -31,6 +32,11 @@ nondeterministic); a saved 🌐 choice still wins. The page carries a static Rus
 pinned to the production origin, JSON-LD, the favicon set and `robots.txt`), while the SPA
 shell is `noindex` — the landing is the only indexable page.
 
+On the plain web the client is an **installable PWA**: a logged-out player sees an install
+call-to-action under the login form (and at the bottom of Settings) that installs the app to the
+home screen / desktop in one tap where the browser supports it (Chromium), or shows manual
+Add-to-Home-Screen steps on iOS Safari; it is hidden once installed and inside the Mini Apps.
+
 ### First-run onboarding
 The first time a player opens the app it walks them through the interface with a light
 **coachmark overlay**: a dimmed layer draws one hint bubble at a time, each pointing — with a

docs/FUNCTIONAL_ru.md

@@ -22,7 +22,8 @@ top-1 подсказку, безлимитную проверку слова с
 Проверка слова принимает только алфавит варианта, запоминает ответы в рамках сессии
 и ограничивает частоту повторов.
 Публичная **посадочная страница** в корне сайта представляет игру, переключает язык и
-тему и ведёт в Telegram-канал игры и в VK Mini App; сама игра живёт по адресам
+тему и ведёт в Telegram-канал игры, в VK Mini App и в **веб-версию** (`/app/`) — каждая под
+подписью (Telegram / VK / Веб-версия); сама игра живёт по адресам
 `/app/` (веб), `/telegram/` (Telegram Mini App) и `/vk/` (VK Mini App). Тема на странице эфемерна (берётся из
 системной настройки, а не из сохранённой), выбор языка сохраняется. Страница всегда
 открывается на **русском** — язык браузера не определяется автоматически (роботы
@@ -33,6 +34,11 @@ Open Graph, которую используют превью ссылок в Tel
 продакшен-домена, JSON-LD, набор favicon и `robots.txt`), а оболочка SPA помечена
 `noindex` — индексируется только посадочная страница.
 
+В обычном вебе клиент — **устанавливаемое PWA**: незалогиненный игрок видит призыв к установке
+под формой входа (и внизу «Настроек»), который в один тап ставит приложение на рабочий стол
+(домашний экран) там, где браузер это умеет (Chromium), либо показывает ручные шаги
+«На экран „Домой“» в Safari на iOS; он скрыт после установки и внутри Mini App.
+
 ### Первый запуск: онбординг
 При первом открытии приложения игрока один раз проводят по интерфейсу лёгким
 **coachmark-оверлеем**: затемнённый слой показывает по одной подсказке-«облачку» за раз, каждое