feat(telegram): split connector into home validator + remote bot

Move all Telegram egress off the main host. The single connector held the
bot token, long-polled Telegram and answered the gateway/backend over the
trusted internal network, so the whole component (including login validation)
shared fate with its VPN sidecar. Split it into two binaries that share the
token:

- cmd/validator (home, no VPN): Mini App initData + Login Widget HMAC only,
  never calls the Bot API. The gateway dials it for Telegram auth, so game
  login is now independent of Telegram reachability.
- cmd/bot (remote): Bot API long-poll + sendMessage, the only component
  reaching Telegram. It holds no inbound port — it dials the gateway over a
  new reverse mTLS bot-link (pkg/proto/botlink/v1) and executes the send
  commands the gateway pushes.

The gateway funnels sends to the bot-link: out-of-app push is fire-and-forget
(at-most-once, dropped if no bot is connected); the backend admin broadcasts
reach a gateway-served relay that forwards them and awaits the bot's ack
(SendToUser/SendToGameChannel contract preserved). mTLS (pkg/mtls) is the one
inter-service link that leaves the trusted segment; validator<->gateway and
the relay stay plaintext internal. The bot is Telegram-rate-limited.

One bot now; the gateway bot registry, an owns_updates flag and per-command
ids leave seams for N later. Webhook rejected (one URL per token, adds inbound
+ a static address).

The unified test contour runs the split (the bot keeps its VPN sidecar and
dials the gateway by its internal name; bot-link certs from deploy/gen-certs.sh,
generated in CI). The prod wiring — the bot on a separate host (no VPN), the
gateway bot-link port published, PROD_ certs with scheduled rotation, an SSH
deploy of both hosts together — is the deferred final stage (PRERELEASE.md TX,
Stage 18).

Docs: ARCHITECTURE, PRERELEASE (phase TX), platform/telegram + gateway +
backend + deploy READMEs, FUNCTIONAL(+ru), CLAUDE.md, .env.example.

platform/telegram/internal/validator/server_test.go

@@ -0,0 +1,63 @@
+package validator
+
+import (
+	"context"
+	"testing"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+
+	telegramv1 "scrabble/pkg/proto/telegram/v1"
+	"scrabble/platform/telegram/internal/initdata"
+	"scrabble/platform/telegram/internal/loginwidget"
+)
+
+// stubValidator returns a fixed user / error from Validate.
+type stubValidator struct {
+	user initdata.User
+	err  error
+}
+
+func (s stubValidator) Validate(string) (initdata.User, error) { return s.user, s.err }
+
+// stubWidgetValidator returns a fixed user / error from the Login Widget Validate.
+type stubWidgetValidator struct {
+	user loginwidget.User
+	err  error
+}
+
+func (s stubWidgetValidator) Validate(string) (loginwidget.User, error) { return s.user, s.err }
+
+func TestValidateInitData(t *testing.T) {
+	want := initdata.User{ExternalID: "42", Username: "neo", FirstName: "Thomas", LanguageCode: "en-GB"}
+	srv := NewServer(stubValidator{user: want}, stubWidgetValidator{})
+	resp, err := srv.ValidateInitData(context.Background(), &telegramv1.ValidateInitDataRequest{InitData: "x"})
+	if err != nil {
+		t.Fatalf("validate: %v", err)
+	}
+	if resp.GetExternalId() != "42" || resp.GetUsername() != "neo" || resp.GetFirstName() != "Thomas" || resp.GetLanguageCode() != "en-GB" {
+		t.Errorf("resp = %+v, want %+v", resp, want)
+	}
+
+	bad := NewServer(stubValidator{err: initdata.ErrInvalidInitData}, stubWidgetValidator{})
+	if _, err := bad.ValidateInitData(context.Background(), &telegramv1.ValidateInitDataRequest{}); status.Code(err) != codes.InvalidArgument {
+		t.Errorf("err code = %v, want InvalidArgument", status.Code(err))
+	}
+}
+
+func TestValidateLoginWidget(t *testing.T) {
+	want := loginwidget.User{ExternalID: "42", Username: "neo", FirstName: "Thomas"}
+	srv := NewServer(stubValidator{}, stubWidgetValidator{user: want})
+	resp, err := srv.ValidateLoginWidget(context.Background(), &telegramv1.ValidateLoginWidgetRequest{Data: "x"})
+	if err != nil {
+		t.Fatalf("validate: %v", err)
+	}
+	if resp.GetExternalId() != "42" || resp.GetUsername() != "neo" || resp.GetFirstName() != "Thomas" {
+		t.Errorf("resp = %+v, want %+v", resp, want)
+	}
+
+	bad := NewServer(stubValidator{}, stubWidgetValidator{err: loginwidget.ErrInvalidLoginWidget})
+	if _, err := bad.ValidateLoginWidget(context.Background(), &telegramv1.ValidateLoginWidgetRequest{}); status.Code(err) != codes.InvalidArgument {
+		t.Errorf("err code = %v, want InvalidArgument", status.Code(err))
+	}
+}