mapAnalyticsToOtlp maps token/cost/activity aggregates to the OTLP/HTTP JSON
envelope (counters + gauges, model/provider/node/agent attributes); a periodic
dashboard exporter is opt-in via FUSION_OTEL_METRICS_ENDPOINT, https-validated,
header-redacted, backs off on failure, and never blocks startup/shutdown.
Minimal exporter (no SDK dep) — real @opentelemetry SDK is a follow-up.