Stage 17 round 6 (#13/About): About screen content + app version from git describe

- About screen: prominent localized title (Scrabble / Эрудит (Скрэббл)), a rules link
  (en/ru Wikipedia), and the Random-game / Game-with-friends sections; copy lives in a
  shared aboutContent module (the landing will reuse it). The random-game move limit
  inlines the 24h auto-match clock.
- App version: Vite define __APP_VERSION__ from VITE_APP_VERSION (default 'dev'), wired as
  a Docker build-arg sourced from `git describe --tags --always` in the deploy step — no
  manual version bumps. The fallback keeps a plain/local build working.

gateway/Dockerfile

@@ -17,12 +17,15 @@ WORKDIR /ui
 RUN corepack enable && corepack prepare pnpm@11.0.9 --activate
 
 # Prod UI build vars (Vite reads VITE_-prefixed env at build; baked into the bundle).
+# VITE_APP_VERSION carries `git describe` for the About screen (defaults to "dev").
 ARG VITE_TELEGRAM_BOT_ID=
 ARG VITE_TELEGRAM_LINK=
 ARG VITE_GATEWAY_URL=
+ARG VITE_APP_VERSION=
 ENV VITE_TELEGRAM_BOT_ID=$VITE_TELEGRAM_BOT_ID \
     VITE_TELEGRAM_LINK=$VITE_TELEGRAM_LINK \
-    VITE_GATEWAY_URL=$VITE_GATEWAY_URL
+    VITE_GATEWAY_URL=$VITE_GATEWAY_URL \
+    VITE_APP_VERSION=$VITE_APP_VERSION
 
 # Install with the lockfile first (the workspace file carries pnpm's build-script
 # approval for esbuild), then build. Committed src/gen/ means no codegen here.