R6(a): de-stage code, docs, READMEs; split stage6_test

Mechanical, behaviour-preserving removal of Stage N / TODO-N / phase (RN)
references from comments, doc-comments, service READMEs, the current-state docs
(ARCHITECTURE, FUNCTIONAL+_ru, TESTING, UI_DESIGN), config-file comments, and the
.fbs/.proto schema comments. PLAN.md / PRERELEASE.md / CLAUDE.md keep the stage
history.

- Rename the only stage-named identifiers: registerStage8 -> registerSocialOps,
  registerStage11 -> registerLinkOps (gateway transcode).
- Split stage6_test.go: TestEmailLoginFlow -> email_test.go,
  TestGuestAutoMatchLeavesNoStats (+ provisionGuest) -> account_test.go.
- Regenerated proto bindings (push.pb.go, telegram_grpc.pb.go) from the de-staged
  .proto comments; FB Go/TS bindings unchanged (flatc strips schema comments).

go build/vet/gofmt clean across modules; integration typecheck and pnpm check green.

platform/telegram/internal/connector/server.go

@@ -1,6 +1,6 @@
 // Package connector implements the Telegram gRPC service (pkg/proto/telegram/v1):
 // the gateway calls ValidateInitData (Mini App auth) and Notify (out-of-app push);
-// the admin surface (Stage 10) calls SendToUser and SendToGameChannel. The generic
+// the admin surface calls SendToUser and SendToGameChannel. The generic
 // methods address a recipient by the identity external_id, so a future platform
 // connector can implement the same service.
 //
@@ -99,7 +99,7 @@ func (s *Server) ValidateInitData(ctx context.Context, req *telegramv1.ValidateI
 
 // ValidateLoginWidget verifies Login Widget authorization data against each bot's
 // token in turn and returns the user identity, for attaching a Telegram identity to
-// an existing account (Stage 11).
+// an existing account.
 func (s *Server) ValidateLoginWidget(ctx context.Context, req *telegramv1.ValidateLoginWidgetRequest) (*telegramv1.ValidateLoginWidgetResponse, error) {
 	var lastErr error
 	for _, lang := range s.order {