feat(core): OTLP trace exporter

[ephor]

Summary

• Adds a generic trace-exporter mechanism to @getvision/core: a TraceExporter interface plus VisionServerOptions.exporters. Completed traces fan out in completeTrace (each exporter isolated — a failing sink never affects request handling) and are flushed on stop().
• Ships OtlpTraceExporter — OTLP/JSON over HTTP with batching. Works with any OTLP-compatible backend (BetterStack, Honeycomb, Grafana Tempo, Datadog, an OTel Collector); the destination is purely endpoint + headers.
• Maps Vision's model to OTLP: each HTTP request becomes a synthetic root SERVER span, c.span(...) calls become nested INTERNAL spans, trace logs become span events. Span/trace ids are random and spec-compliant via Web Crypto (no node: import, no hashing — cross-runtime).
• @getvision/server: forwards vision.exporters into VisionCore and re-exports OtlpTraceExporter.
• Docs: package README + docs-site config/section; roadmap marks "OpenTelemetry export" as shipped.

Usage

import { createVision, OtlpTraceExporter } from '@getvision/server'

createVision({
  service: { name: 'my-api' },
  vision: {
    exporters: [
      new OtlpTraceExporter({
        endpoint: 'https://<host>/v1/traces',
        headers: { Authorization: 'Bearer <token>' },
        serviceName: 'my-api',
      }),
    ],
  },
})

Test plan

• @getvision/core unit tests for the Trace → OTLP transform (id format, span reparenting, status mapping, logs-as-events, payload shape) — 11/11 pass
• @getvision/server API-contract test (exporter reachable + config accepts TraceExporter[])
• bun test / bun run typecheck:test in CI (server tests can't run in the dev sandbox — deps not installed)
• Manual smoke: point endpoint at a real OTLP backend and confirm traces arrive