feat(edge): community IP blocklist (Spamhaus DROP) at the gateway

Refuse a client whose IP is in a curated CIDR feed with 403 in the same
abuseGuard, before the fail2ban ban. Prod-only (keys by real client IP), off by
default.

- ratelimit.Blocklist: a sorted-range IPv4 matcher (binary search) with an
  allowlist checked first; ParseDROP reads the feed; ApplyRefresh keeps the
  last-good feed on a transient fetch failure and drops it fail-open once stale
  (better to under-block than block a legitimate client on a frozen feed). A
  separate static CIDR set, not the per-IP fail2ban store.
- gateway: a refresher goroutine re-fetches every few hours (bounded fetch + size
  cap); config GATEWAY_BLOCKLIST_{ENABLED,URL,ALLOW,REFRESH,MAX_STALENESS}.
  IPv6 is not matched (a v6 client is still covered by fail2ban / the honeypot).
- observability: gateway_blocklist_blocked_total + entries/age gauges; a Grafana
  alert warns before the feed is dropped; service-overview panels.
- deploy: compose env + write-prod-env.sh + prod-deploy/rollback wiring (opt-in
  via PROD_ vars).
- docs (ARCHITECTURE, deploy/README); unit tests (match, allowlist, IPv6 skip,
  parser, fault-tolerance) + a 403 abuse-guard integration test.

gateway/internal/connectsrv/metrics_test.go

@@ -16,7 +16,7 @@ func TestEdgeMetric(t *testing.T) {
 	ctx := context.Background()
 	reader := sdkmetric.NewManualReader()
 	meter := sdkmetric.NewMeterProvider(sdkmetric.WithReader(reader)).Meter("test")
-	m := newServerMetrics(meter)
+	m := newServerMetrics(meter, nil)
 
 	m.recordEdge(ctx, "game.submit_play", "ok", time.Now().Add(-time.Millisecond))
 	m.recordEdge(ctx, "game.submit_play", "ok", time.Now().Add(-time.Millisecond))
@@ -74,7 +74,7 @@ func TestRateLimitedMetric(t *testing.T) {
 	ctx := context.Background()
 	reader := sdkmetric.NewManualReader()
 	meter := sdkmetric.NewMeterProvider(sdkmetric.WithReader(reader)).Meter("test")
-	m := newServerMetrics(meter)
+	m := newServerMetrics(meter, nil)
 
 	m.recordRateLimited(ctx, "user")
 	m.recordRateLimited(ctx, "user")
@@ -112,7 +112,7 @@ func TestBannedMetric(t *testing.T) {
 	ctx := context.Background()
 	reader := sdkmetric.NewManualReader()
 	meter := sdkmetric.NewMeterProvider(sdkmetric.WithReader(reader)).Meter("test")
-	m := newServerMetrics(meter)
+	m := newServerMetrics(meter, nil)
 
 	m.recordBan(ctx, "tripwire")
 	m.recordBan(ctx, "tripwire")
@@ -150,7 +150,7 @@ func TestUnsupportedEngineMetric(t *testing.T) {
 	ctx := context.Background()
 	reader := sdkmetric.NewManualReader()
 	meter := sdkmetric.NewMeterProvider(sdkmetric.WithReader(reader)).Meter("test")
-	m := newServerMetrics(meter)
+	m := newServerMetrics(meter, nil)
 
 	m.recordUnsupportedEngine(ctx, "no_bigint", "66")
 	m.recordUnsupportedEngine(ctx, "no_bigint", "66")