Add pluggable observability infrastructure that supports any OTLP-compatible backend (Jaeger, Axiom, Grafana, Honeycomb). Disabled by default with zero overhead when not enabled. Changes: - Add internal/observability package with config, provider, and middleware - Integrate tracing into main.go with graceful shutdown - Add Jaeger service to docker-compose with 'observability' profile - Add `make dev-up-otel` for local tracing with Jaeger UI - Document OTEL_* environment variables in example files - Add OpenTelemetry SDK dependencies (otel, otlptracegrpc, otelhttp) Usage: make dev-up-otel # Start dev stack with Jaeger OTEL_ENABLED=true OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4317 make run Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>