feat(ops): protect metrics, rate-limit auth, agent secret timing, e2e smoke

Bearer для /metrics (EVOBGP_METRICS_TOKEN); rate limit /v1/auth/config; constant-time agent secret; OTel stub; Playwright smoke; HTTP_PROXY note; checklist обновлён.

Co-authored-by: Cursor <[email protected]>

internal/observability/otel.go

@@ -0,0 +1,21 @@
+package observability
+
+import (
+	"context"
+	"os"
+	"strings"
+
+	"evobgp/internal/logging"
+)
+
+// StartOTelIfEnabled is an opt-in stub for OpenTelemetry (EVOBGP_OTEL_ENDPOINT).
+// Full exporter wiring lands when the ops stack provides a collector; this logs intent only.
+func StartOTelIfEnabled(ctx context.Context) (shutdown func(context.Context) error) {
+	ep := strings.TrimSpace(os.Getenv("EVOBGP_OTEL_ENDPOINT"))
+	if ep == "" {
+		return func(context.Context) error { return nil }
+	}
+	logging.Default().Info("otel opt-in enabled (stub; export not wired yet)", "endpoint", ep)
+	_ = ctx
+	return func(context.Context) error { return nil }
+}