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.

backend/cmd/backend/main.go

@@ -20,6 +20,7 @@ import (
 	"scrabble/backend/internal/account"
 	"scrabble/backend/internal/accountmerge"
 	"scrabble/backend/internal/ads"
+	"scrabble/backend/internal/banview"
 	"scrabble/backend/internal/config"
 	"scrabble/backend/internal/connector"
 	"scrabble/backend/internal/engine"
@@ -211,6 +212,10 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 		zap.Int("flag_threshold", cfg.RateWatch.FlagThreshold),
 		zap.Duration("flag_window", cfg.RateWatch.FlagWindow))
 
+	// Ban observability: mirror the gateway's active IP bans for the admin console's
+	// active-bans panel and collect operator unban requests.
+	banView := banview.New()
+
 	// Advertising-banner domain: campaign rotation feeding the profile.get banner
 	// block and the banner admin console section.
 	adsSvc := ads.NewService(ads.NewStore(db))
@@ -233,6 +238,7 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 		DictDir:       cfg.Game.DictDir,
 		Connector:     conn,
 		RateWatch:     rateWatch,
+		BanView:       banView,
 		Ads:           adsSvc,
 		Notifier:      hub,
 	})