Redesign SpanGuard with pimpl idiom to hide all OpenTelemetry types
from public headers. Add global Telemetry accessor so SpanGuard factory
methods work without explicit Telemetry references. Add child/linked
span creation and cross-thread context propagation. Update plan docs
to reflect macro removal in favor of SpanGuard factory pattern.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Tempo is now the sole trace backend. Remove Jaeger all-in-one service
from docker-compose, otlp/jaeger exporter from OTel Collector config,
and Jaeger Grafana datasource provisioning file.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>