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/README.md

@@ -148,6 +148,13 @@ rejected calls within `BACKEND_HIGHRATE_FLAG_WINDOW` gets the soft, reversible
 `accounts.flagged_high_rate_at` marker (set-once; a badge in the user list and a
 **Clear** action on the user card; never an automatic ban).
 
+The gateway also syncs its active IP bans (prod-only — see ARCHITECTURE §11) to
+`POST /api/v1/internal/bans/sync`; `internal/banview` mirrors them for the console's
+**Throttled** page (an **Active IP bans** panel with an **Unban** action) and returns
+the operator's pending unbans in the response, which the gateway applies on its next
+sync. Like `ratewatch` it is in-memory and resets on restart — the enforced ban lives
+in the gateway, not here.
+
 ## Package layout
 
 ```
@@ -173,6 +180,7 @@ internal/adminconsole/ # server-rendered admin console (Go templates + embedded
 internal/ads/        # advertising banner: campaigns + bilingual messages + display timings, weighted-rotation feed (ActiveSet)
 internal/connector/  # backend gRPC client to the gateway bot-link relay (operator broadcasts)
 internal/ratewatch/  # gateway rate-limit reports: episode window for the console + the high-rate auto-flag
+internal/banview/    # gateway active-ban mirror: the console's Active IP bans panel + the operator unban backchannel
 ```
 
 ## Configuration (environment)