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/internal/server/server.go

@@ -20,6 +20,7 @@ import (
 	"scrabble/backend/internal/account"
 	"scrabble/backend/internal/adminconsole"
 	"scrabble/backend/internal/ads"
+	"scrabble/backend/internal/banview"
 	"scrabble/backend/internal/connector"
 	"scrabble/backend/internal/engine"
 	"scrabble/backend/internal/feedback"
@@ -83,6 +84,10 @@ type Deps struct {
 	// admin console's throttled view + the high-rate auto-flag. A nil RateWatch
 	// disables the internal report endpoint and the console view.
 	RateWatch *ratewatch.Watch
+	// BanView mirrors the gateway's active IP bans for the admin console and
+	// collects operator unban requests. A nil BanView disables the internal
+	// ban-sync endpoint and the console's active-bans panel.
+	BanView *banview.View
 	// Ads is the advertising-banner domain service: campaign rotation feeding the
 	// profile.get banner block, plus the banner admin console section. A nil Ads
 	// omits the banner block and disables the banner console.
@@ -115,6 +120,7 @@ type Server struct {
 	dictDir     string
 	connector   *connector.Client
 	ratewatch   *ratewatch.Watch
+	banview     *banview.View
 	ads         *ads.Service
 	notifier    notify.Publisher
 	console     *adminconsole.Renderer
@@ -164,6 +170,7 @@ func New(addr string, deps Deps) *Server {
 		dictDir:       deps.DictDir,
 		connector:     deps.Connector,
 		ratewatch:     deps.RateWatch,
+		banview:       deps.BanView,
 		ads:           deps.Ads,
 		notifier:      notifier,
 		http:          &http.Server{Addr: addr, Handler: engine},