docs(voyage): add docs/observability.md — operator quickstart for v4.1 OTel export
Step 15 of v4.1 — operator-facing observability docs (151 lines, target ≥80).
Sections:
- Overview (JSONL is default, OTel is opt-in)
- Activating OTel export (VOYAGE_EXPORT_MODE)
- Output formats (Prometheus textfile vs OTLP/HTTP)
- Environment variables matrix
- Docker Compose quickstart (cross-link to examples/observability/)
- Stats schema (cross-link to tests/fixtures/jsonl-schemas.md)
- Security (CWE-22, CWE-918, CWE-212 mitigations + min-versions per CVE)
- Limitations (Stop-hook normal-exit only, no retry, NFR best-effort)
- Cost-estimering disclaimer (per brief Risk-tabell)
Kjell Tore Guttormsen
7e60b28c8d