legion-observability

See everything Legion does and close the self-learning loop. Unified legion.span.v1 telemetry, legion-report cost/success/latency, legion-bench deterministic core/stable harness benchmarks plus A/B corpus runs with repeated-run flake detection, legion-catalog marketplace inventory, legion-self-learn daily failure mining + command/agent/skill improvement memory/proposals, legion-trace, legion-otel-export, and legion-doctor install verification.