Stage 11: account linking & merge (email + Telegram Login Widget)

Link an email (confirm-code) or Telegram (web Login Widget) to the current
account; if the identity already has its own account, merge the two into the
one in use (the current account is primary, except a guest initiator whose
durable counterpart wins). The merge runs in one transaction
(internal/accountmerge): stats + hint wallet summed, paid_account ORed,
identities/games/chat/complaints transferred, friends/blocks de-duplicated,
the secondary kept as a merged_into tombstone so a shared finished game's
no-cascade FKs hold; a shared active game blocks the merge.

- migration 00009: accounts.paid_account, merged_into, merged_at (+ jetgen)
- internal/link orchestrator; session.RevokeAllForAccount on merge
- connector ValidateLoginWidget RPC + loginwidget HMAC validator
- edge ops link.email.request/confirm/merge, link.telegram.confirm/merge;
  supersedes the Stage 8 email.bind.* surface (request never reveals 'taken'
  before the code is verified, so a probe cannot enumerate addresses)
- UI Profile link section + irreversible-merge dialog; Telegram web sign-in
- focused regression tests (merge core, guest inversion, active-game refusal,
  finished-shared-game kept), gateway transcode + connector + UI codec/e2e
- docs: PLAN, ARCHITECTURE 3/4/9, FUNCTIONAL(+ru), module READMEs

backend/internal/server/handlers_admin_console.go

@@ -110,8 +110,11 @@ func (s *Server) consoleUserDetail(c *gin.Context) {
 	view := adminconsole.UserDetailView{
 		ID: acc.ID.String(), DisplayName: acc.DisplayName, Language: acc.PreferredLanguage,
 		TimeZone: acc.TimeZone, Guest: acc.IsGuest, NotificationsInAppOnly: acc.NotificationsInAppOnly,
-		HintBalance: acc.HintBalance, CreatedAt: fmtTime(acc.CreatedAt), HasStats: !acc.IsGuest,
-		ConnectorEnabled: s.connector != nil,
+		PaidAccount: acc.PaidAccount, HintBalance: acc.HintBalance, CreatedAt: fmtTime(acc.CreatedAt),
+		HasStats: !acc.IsGuest, ConnectorEnabled: s.connector != nil,
+	}
+	if acc.MergedInto != uuid.Nil {
+		view.MergedInto = acc.MergedInto.String()
 	}
 	if view.HasStats {
 		if st, err := s.accounts.GetStats(ctx, id); err == nil {