Add OpenTelemetry observability integration

[PAMulligan]

Description

Add OpenTelemetry (OTel) integration as an optional observability layer for generated APIs. This provides distributed tracing, metrics, and structured logging out of the box.

Why

Observability is essential for production APIs. OpenTelemetry is the industry standard for instrumentation — supporting it means Nerva-generated APIs can export telemetry to Jaeger, Grafana, Datadog, Honeycomb, or any OTel-compatible backend without vendor lock-in.

Acceptance Criteria

• Create a Hono middleware that:
  • Creates spans for each HTTP request (method, path, status code, duration)
  • Propagates trace context headers (W3C Trace Context)
  • Records errors as span events
  • Adds custom attributes (request ID, user ID if authenticated)
• Add `@opentelemetry/api` and relevant SDK packages
• Create a trace configuration template (`tracing.ts`) with:
  • Console exporter for development
  • OTLP exporter for production
  • Automatic span batching and sampling
• Add optional `--otel` flag to `setup-project.sh`
• Create a new `monitoring` skill documenting OTel setup
• Include a docker-compose service for Jaeger (local development)
• CI passes

Notes

For Cloudflare Workers, use the Workers-compatible OTel SDK (`@microlabs/otel-cf-workers` or similar).

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