OpenTelemetry tracing

[carole-lavillonniere]

Motivation

Add end-to-end distributed tracing to lstk so developers can inspect the full call tree of any command — Docker API calls, platform API calls, emulator health checks — in a local Jaeger (or any OTLP-compatible) backend.

Closes DRG-410

Changes

• internal/tracing: new package that initialises the global OTel TracerProvider; exports spans via OTLP/HTTP; silently no-ops when no collector is reachable
• cmd/root.go: wrapCommandsWithTracing recursively wraps every Cobra RunE with an lstk.<command> root span; sets lstk.exit_code attribute; shuts down the provider with a fresh context on exit to flush buffered spans even after Ctrl+C
• Docker instrumentation: hooks into the Docker SDK's WithTraceOptions to override the default span name formatter with a docker prefix, avoiding the triple-wrapping that would result from adding a second otelhttp layer
• Platform API instrumentation: NewPlatformClient wraps its transport with platform prefixed spans
• AWS emulator instrumentation: aws.NewClient() (no longer takes *http.Client) owns its OTel-wrapped transport with aws prefixed spans
• Startup health check instrumentation: awaitStartup instruments its polling HTTP client with an emulator-type prefix (e.g. aws GET /_localstack/health), making the readiness polling loop visible in traces
• Resource attributes: service.name, service.version, os.type, host.arch on all spans
• LSTK_OTLP_ENDPOINT: new env var (default http://localhost:4318); TLS used automatically for https:// endpoints
• docker-compose.tracing.yaml: one-command Jaeger setup for local development

Tests

Manually verified with docker compose -f docker-compose.tracing.yaml up -d and lstk start / lstk status. Traces appear in Jaeger at http://localhost:16686 with correct span hierarchy and names. Existing unit and integration tests pass unchanged.