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.

backend/internal/adminconsole/render_test.go

@@ -24,6 +24,7 @@ func TestRendererRendersEveryPage(t *testing.T) {
 		{"dashboard", DashboardView{Accounts: 3, Variants: []VariantVersions{{Variant: "scrabble_en", Latest: "v1", Versions: []string{"v1"}}}}, "Dashboard"},
 		{"users", UsersView{Items: []UserRow{{ID: "a1", DisplayName: "Kaya", FlaggedHighRate: true}}, Pager: NewPager(1, 50, 1)}, "high-rate"},
 		{"user_detail", UserDetailView{ID: "a1", DisplayName: "Kaya", HasStats: true, Stats: StatsRow{Wins: 2}, TelegramID: "123", ConnectorEnabled: true}, "Send Telegram message"},
+		{"user_detail", UserDetailView{ID: "a1", DisplayName: "Kaya", VKID: "494075"}, "vk.com/id494075"},
 		{"user_detail", UserDetailView{ID: "a1", DisplayName: "Kaya", FlaggedHighRateAt: "2026-06-10 12:00"}, "Clear high-rate flag"},
 		{"user_detail", UserDetailView{ID: "a1", DisplayName: "Kaya", Roles: []string{"feedback_banned"}, KnownRoles: []string{"feedback_banned"}}, "feedback_banned"},
 		{"user_detail", UserDetailView{ID: "a1", DisplayName: "Kaya",

backend/internal/adminconsole/templates/pages/user_detail.gohtml

@@ -142,6 +142,11 @@
 {{else}}<p class="note">connector not configured (set BACKEND_CONNECTOR_ADDR)</p>{{end}}
 </section>
 {{end}}
+{{if .VKID}}
+<section class="panel"><h2>VK</h2>
+<p>VK ID: <code>{{.VKID}}</code> · <a href="https://vk.com/id{{.VKID}}" target="_blank" rel="noopener">open profile</a></p>
+</section>
+{{end}}
 <section class="panel"><h2>Games</h2>
 <table class="list">
 <thead><tr><th>Game</th><th>Variant</th><th>Status</th><th class="num">Players</th><th>Updated</th></tr></thead>

backend/internal/adminconsole/views.go

@@ -156,13 +156,17 @@ type UserDetailView struct {
 	HintBalance       int
 	// HintGrantMax is the per-grant cap the operator's "add hints" form enforces (it mirrors the
 	// server's maxHintGrant), passed through so the policy value lives in one place.
-	HintGrantMax     int
-	CreatedAt        string
-	HasStats         bool
-	Stats            StatsRow
-	Identities       []IdentityRow
-	Games            []GameRow
+	HintGrantMax int
+	CreatedAt    string
+	HasStats     bool
+	Stats        StatsRow
+	Identities   []IdentityRow
+	Games        []GameRow
+	// TelegramID and VKID are the account's platform external ids (empty when absent).
+	// TelegramID gates the "Send Telegram message" operator action; VKID surfaces the VK
+	// user id with a link to the VK profile (there is no VK messaging to drive).
 	TelegramID       string
+	VKID             string
 	ConnectorEnabled bool
 	// MoveChart is the pre-rendered inline SVG of the account's per-move-number think
 	// time (min/mean/max), empty when the account has no timed move.