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.

deploy/README.md

@@ -13,7 +13,7 @@ operational reference for **every environment variable**.
 | --- | --- | --- |
 | `caddy` | `caddy:2-alpine` | Edge proxy (alias `scrabble` on `edge`): single `/_gm` Basic-Auth → admin console + Grafana; `/app/`, `/telegram/` + the Connect path → gateway; the catch-all (incl. `/`) → landing. TLS per `CADDY_SITE_ADDRESS`. |
 | `gateway` | built (`gateway/Dockerfile`, target `gateway`) | Public edge; serves the embedded game SPA at `/app/` + `/telegram/`; Connect-RPC edge. `/` redirects to `/app/`. |
-| `landing` | built (`gateway/Dockerfile`, target `landing`) | Static landing page at `/` (caddy:2-alpine + the shared Vite build, `deploy/landing/Caddyfile`); absorbs stray public paths (R3). |
+| `landing` | built (`gateway/Dockerfile`, target `landing`) | Static landing page at `/` (caddy:2-alpine + the shared Vite build, `deploy/landing/Caddyfile`); absorbs stray public paths. |
 | `backend` | built (`backend/Dockerfile`) | Domain service; bakes in the DAWG dictionaries; runs migrations at boot. |
 | `postgres` | `postgres:17-alpine` | Database (named volume, `pg_isready` healthcheck). |
 | `vpn` + `telegram` | sidecar + built (`platform/telegram/Dockerfile`) | Telegram connector; egresses through the AmneziaWG sidecar; internal gRPC at `telegram:9091`. |
@@ -39,7 +39,7 @@ cd deploy && docker compose up -d --build
 
 **In CI** (the test contour) — `.gitea/workflows/ci.yaml`'s `deploy` job maps the
 Gitea **`TEST_`-prefixed** secrets/variables onto the unprefixed names below and
-runs `docker compose up -d --build` on the runner host. Stage 18 (prod) maps the
+runs `docker compose up -d --build` on the runner host. The prod deploy maps the
 **`PROD_`** set the same way. So a Gitea secret named `TEST_POSTGRES_PASSWORD`
 feeds the compose's `POSTGRES_PASSWORD`, etc.
 
@@ -80,7 +80,7 @@ connector **fails at boot** if both are empty.
 | `GRAFANA_ADMIN_PASSWORD` | secret | `admin` | Grafana admin password. Low impact (the login form is disabled, access is anonymous-admin behind caddy) but set it anyway. |
 | `TELEGRAM_GAME_CHANNEL_ID_EN` | variable | _(empty)_ | English game-channel id; empty/`0` disables channel posts. |
 | `TELEGRAM_GAME_CHANNEL_ID_RU` | variable | _(empty)_ | Russian game-channel id; empty/`0` disables channel posts. |
-| `TELEGRAM_TEST_ENV` | _pinned_ | `false` | `true` routes the bot through Telegram's test environment (`.../bot<token>/test/METHOD`). **The CI test contour pins this to `true` in `ci.yaml`** (the contour is the test environment) — it is not a Gitea variable. Set it in `.env` for a local run; prod (Stage 18) leaves it `false`. |
+| `TELEGRAM_TEST_ENV` | _pinned_ | `false` | `true` routes the bot through Telegram's test environment (`.../bot<token>/test/METHOD`). **The CI test contour pins this to `true` in `ci.yaml`** (the contour is the test environment) — it is not a Gitea variable. Set it in `.env` for a local run; prod leaves it `false`. |
 | `TELEGRAM_API_BASE_URL` | variable | _(empty)_ | Override the Bot API host (a mock/self-hosted server); empty = `https://api.telegram.org`. |
 | `GATEWAY_DEFAULT_SUPPORTED_LANGUAGES` | variable | `en,ru` | Variant-gating set for non-Telegram logins (web/email/guest). |
 | `VITE_TELEGRAM_BOT_ID` | variable | _(empty)_ | UI build-arg: numeric bot id for the web Login Widget. |
@@ -114,7 +114,7 @@ resolves both `otelcol` and `api.telegram.org`. `GATEWAY_ADMIN_*` is intentional
 - **Host caddy** route `<domain> → scrabble:80` (the in-compose caddy serves HTTP
   in the test contour; the host caddy terminates TLS). Not needed on prod, where the
   contour caddy owns TLS (set `CADDY_SITE_ADDRESS` to the domain).
-- **Branch protection** requires the single status check `CI / gate` (Stage 17).
+- **Branch protection** requires the single status check `CI / gate`.
   The `unit` / `integration` / `ui` jobs are path-conditional (they skip when their
   code did not change), and the always-running `gate` job aggregates them (passing
   when each succeeded or was skipped), so a skipped job never blocks a merge. See