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/adminconsole/views.go

@@ -389,17 +389,27 @@ type BroadcastView struct {
 	ConnectorEnabled bool
 }
 
-// ThrottledView is the rate-limit observability page: the recent gateway-reported
-// throttle episodes (in-memory, reset on restart) and the accounts currently
-// carrying the high-rate flag. FlagThreshold and FlagWindow caption the active
-// auto-flag tuning.
+// ThrottledView is the rate-limit observability page: the temporary IP bans the
+// gateway is currently enforcing, the recent gateway-reported throttle episodes
+// (in-memory, reset on restart) and the accounts currently carrying the high-rate
+// flag. FlagThreshold and FlagWindow caption the active auto-flag tuning.
 type ThrottledView struct {
+	Bans          []BanRow
 	Episodes      []ThrottleEpisodeRow
 	Flagged       []FlaggedAccountRow
 	FlagThreshold int
 	FlagWindow    string
 }
 
+// BanRow is one temporary IP ban the gateway is enforcing, with its reason and its
+// since/expiry timestamps; the row carries an unban action.
+type BanRow struct {
+	IP      string
+	Reason  string
+	Since   string
+	Expires string
+}
+
 // ThrottleEpisodeRow is one recently throttled limiter key. UserID links to the
 // user card and is set only for the user class (the other classes key by IP).
 type ThrottleEpisodeRow struct {