feat(gateway): wire GATEWAY_HONEYTOKEN through the deploy

The planted honeytoken bearer trap already existed in the gateway + compose, but
no workflow fed GATEWAY_HONEYTOKEN, so it was always empty (inert). Wire the
per-contour TEST_/PROD_GATEWAY_HONEYTOKEN secret into the ci deploy, prod-deploy
and prod-rollback env (the prod path via the shared deploy/write-prod-env.sh),
document it (deploy/README + .env.example), and fix the stale compose comment.

Empty secret = trap off (no ":?" guard), so a deploy is safe before the operator
sets the value + plants the bait. On prod (IP ban on) presenting it earns a 24h
ban + alarm; on test (ban off) it logs + a ban metric.

GF_SMTP_ENABLED is enabled separately via the TEST_/PROD_GF_SMTP_ENABLED Gitea
variables (=true) — no code change.

.gitea/workflows/prod-rollback.yaml

@@ -63,6 +63,7 @@ jobs:
       GATEWAY_VK_APP_SECRET: ${{ secrets.GATEWAY_VK_APP_SECRET }}
       VITE_VK_APP_ID: ${{ vars.VITE_VK_APP_ID }}
       GATEWAY_VK_ID_CLIENT_SECRET: ${{ secrets.GATEWAY_VK_ID_CLIENT_SECRET }}
+      GATEWAY_HONEYTOKEN: ${{ secrets.PROD_GATEWAY_HONEYTOKEN }}
       EXPORT_SIGN_KEY: ${{ secrets.PROD_EXPORT_SIGN_KEY }}
       SMTP_RELAY_USER: ${{ secrets.SMTP_RELAY_USER }}
       SMTP_RELAY_PASS: ${{ secrets.SMTP_RELAY_PASS }}