Prometheus Metrics

Returns optical telemetry metrics in Prometheus exposition format. No authentication required — designed for Prometheus scraping. Includes per-port (risk>=30) gauges fiber_port_rx_power_dbm, fiber_port_temperature_celsius, fiber_port_risk_score, fiber_port_fec_uncorrectable and fiber_port_snr_db (coherent only), plus the cluster-level fiber_cluster_* gauges (total/critical/warning ports, average risk score). The same ports are additionally exported under the OpenTelemetry hardware semantic conventions (semconv v1.44.0): hw_status with hw_state one of ok|degraded|failed|predicted_failure, plus hw_optical_* gauges (rx/tx power, temperature, bias current, FEC) carrying hw_id/hw_type/hw_parent attributes. The fiber_port_* / fiber_cluster_* families are unchanged; set FIBER_OTEL_HW_SEMCONV=0 to opt out of the hw.* duplicates. See docs/OTEL_SEMCONV.md.