feat(gateway): temporary IP ban (fail2ban) fed by rejections + honeypot/honeytoken

Add a prod-only, in-memory IP ban enforced at the edge, fed by three signals:
sustained rate-limiter rejections (the IP-keyed public/email/admin classes — the
user class stays the backend soft-flag's concern), a honeypot decoy-path hit (the
contour caddy tags decoys with X-Scrabble-Honeypot and routes them to the gateway),
and a honeytoken (a planted bearer, GATEWAY_HONEYTOKEN). A banned IP is refused with
429 by the abuseGuard middleware before any work — covering the Connect edge, the
live stream and the static SPA/landing the per-op limiter never gated.

The ban is off by default: it keys by the real client IP the shared-NAT test contour
does not expose, so a ban there would be self-inflicted; detection still logs in the
contour, only the ban action is gated (GATEWAY_ABUSE_BAN_ENABLED). Rejection bans last
GATEWAY_ABUSE_BAN_DURATION; tripwire/honeytoken hits are near-zero-false-positive and
earn longer fixed bans. Each ban increments gateway_abuse_banned_total{reason}.

Operators see and lift active bans on the admin console's Throttled page; the gateway
syncs its active set to the backend every 30s (POST /api/v1/internal/bans/sync,
backend/internal/banview) and applies the operator unbans the response returns.

PRERELEASE phase AG. Docs baked into ARCHITECTURE / FUNCTIONAL (+ru) / both READMEs.

deploy/docker-compose.yml

@@ -150,6 +150,13 @@ services:
       GATEWAY_BOTLINK_TLS_CERT: /certs/gateway.crt
       GATEWAY_BOTLINK_TLS_KEY: /certs/gateway.key
       GATEWAY_BOTLINK_TLS_CA: /certs/ca.crt
+      # Anti-abuse IP ban (fail2ban-style), fed by rate-limit rejections and the
+      # honeypot/honeytoken. Off by default: it bans by client IP, which is only
+      # real in prod — the test contour arrives as one shared NAT address, so a ban
+      # there would be self-inflicted (the honeypot/honeytoken still log). Prod sets
+      # these from PROD_ inputs; GATEWAY_HONEYTOKEN is the planted bearer trap.
+      GATEWAY_ABUSE_BAN_ENABLED: ${GATEWAY_ABUSE_BAN_ENABLED:-false}
+      GATEWAY_HONEYTOKEN: ${GATEWAY_HONEYTOKEN:-}
       GATEWAY_LOG_LEVEL: ${LOG_LEVEL:-info}
       GATEWAY_SERVICE_NAME: scrabble-gateway
       GATEWAY_OTEL_TRACES_EXPORTER: otlp