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.

CLAUDE.md

@@ -125,9 +125,9 @@ backend/                     # module scrabble/backend
   internal/inttest/          # //go:build integration Postgres-backed tests
 docs/  .gitea/workflows/  PLAN.md  CLAUDE.md  README.md
 gateway/  ui/  pkg/              # added by their stages
-platform/telegram/               # Telegram connector side-service (Stage 9): bot + gRPC API
+platform/telegram/               # Telegram side-service, two binaries (Stage 9; split in phase TX): cmd/validator (HMAC, no VPN) + cmd/bot (Bot API; dials gateway over reverse mTLS bot-link)
 loadtest/                        # module scrabble/loadtest: the pre-release stress harness (R2)
-backend/Dockerfile gateway/Dockerfile platform/telegram/Dockerfile loadtest/Dockerfile  # multi-stage distroless (Stage 16; loadtest R2); gateway/Dockerfile also has the `landing` target (R3)
+backend/Dockerfile gateway/Dockerfile platform/telegram/Dockerfile loadtest/Dockerfile  # multi-stage distroless (Stage 16; loadtest R2); gateway/Dockerfile has the `landing` target (R3), platform/telegram/Dockerfile has `validator`+`bot` targets (TX)
 deploy/                          # docker-compose (per-service limits, R7) + caddy + landing + otelcol (OTLP + docker_stats per-container metrics) + prometheus/tempo/grafana + postgres_exporter
 ```
 
@@ -138,7 +138,7 @@ go build ./backend/...          # per module ('./...' from the root won't span t
 go vet ./backend/...
 gofmt -l .                      # must print nothing
 go test -count=1 ./backend/...
-go build ./platform/telegram/... && go test ./platform/telegram/...  # Telegram connector (Stage 9)
+go build ./platform/telegram/... && go test ./platform/telegram/...  # Telegram validator + bot (Stage 9; split in TX)
 go run ./backend/cmd/backend    # /healthz, /readyz on :8080
 
 cd ui && pnpm install && pnpm check && pnpm test:unit && pnpm build  # the UI (Stage 7+)