feat(vk): embed the game as a VK Mini App

Mirror the Telegram Mini App wrapper for VK: the SPA loads at a new /vk/
entry, authenticates from VK's signed launch parameters, and provisions a
'vk' platform identity — the minimum to run the game in VK test mode.

- Gateway verifies the launch signature in-process (internal/vkauth:
  HMAC-SHA256 over the sorted vk_* params under GATEWAY_VK_APP_SECRET,
  base64url) — a pure offline check, no side-service. New auth.vk op
  (gated on the secret), backendclient.VKAuth, /vk/ SPA mount.
- Backend: KindVK + ProvisionVK/vkSeed, /sessions/vk handler, identity
  kind widened to include 'vk' (migration 00005, expand-contract).
- UI: src/lib/vk.ts (VK Bridge, lazy-imported), bootVK + the /vk/ boot
  dispatch, encodeVKLogin + authVK across transport/client/mock. VK omits
  the name from the signed params, so the client reads it via
  VKWebAppGetUserInfo as an unsigned display seed.
- Deploy: /vk in the edge Caddyfile, GATEWAY_VK_APP_SECRET wired through
  compose + .env.example + CI (TEST_) + prod-deploy (PROD_).
- Admin console: surface the VK user id (link to the VK profile) next to
  the Telegram id on the user card.
- Docs: ARCHITECTURE §12/§13, FUNCTIONAL (+ _ru), gateway README; VK
  integration reference under .claude/.

Signature algorithm verified against dev.vk.com plus independent Node/Python
references and a %2C edge-case vector.

gateway/internal/connectsrv/server.go

@@ -183,14 +183,15 @@ func (s *Server) HTTPHandler() http.Handler {
 		// does not serve the app shell at the operator path.
 		mux.Handle("/_gm/", http.NotFoundHandler())
 	}
-	// The embedded UI: the game SPA under /app/ (web) and /telegram/ (the Telegram
-	// Mini App) — the single-origin model (docs/ARCHITECTURE.md §13). Both sit below
-	// the h2c wrap so the Connect edge (a more specific prefix) keeps priority, and
-	// each mount falls back to the app shell (index.html) for the hash router. The
-	// public landing lives in its own static container behind the contour caddy,
-	// so the catch-all redirects a stray root hit to the app shell — which
-	// keeps a local no-caddy run usable.
+	// The embedded UI: the game SPA under /app/ (web), /telegram/ (the Telegram Mini
+	// App) and /vk/ (the VK Mini App) — the single-origin model (docs/ARCHITECTURE.md
+	// §13). All sit below the h2c wrap so the Connect edge (a more specific prefix) keeps
+	// priority, and each mount falls back to the app shell (index.html) for the hash
+	// router. The public landing lives in its own static container behind the contour
+	// caddy, so the catch-all redirects a stray root hit to the app shell — which keeps a
+	// local no-caddy run usable.
 	mux.Handle("/telegram/", webui.Handler("/telegram/", "index.html"))
+	mux.Handle("/vk/", webui.Handler("/vk/", "index.html"))
 	mux.Handle("/app/", webui.Handler("/app/", "index.html"))
 	mux.Handle("/", http.RedirectHandler("/app/", http.StatusPermanentRedirect))
 	// abuseGuard is the outermost wrap (right under h2c) so a banned IP or a