docs: commit all Phase 6 documentation updates and OpenSpec archives

- devops docs: 8 files updated for Phase 6 state; field-trial.md added (946-line runbook)
- developer docs: api-reference (50+ endpoints), quick-start, 5 existing guides updated, 5 new guides added
- engineering docs: all 12 files updated (services, architecture, SDK guide, testing, overview)
- OpenSpec archives: phase-7-devops-field-trial, developer-docs-phase6-update, engineering-docs-phase6-update
- VALIDATOR.md + scripts/start-validator.sh: V&V Architect tooling added
- .gitignore: exclude session artifacts, build artifacts, and agent workspaces

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -6,6 +6,7 @@
 **Git Repository**: https://git.sentryagent.ai/  
 **AI Partner**: Anthropic (Claude — All Development, Implementation & Deployment)  
 **Standards**: AGNTCY (Linux Foundation), OpenAPI 3.0, OAuth 2.0, OIDC  
+**Document Role**: Product Requirements Document (PRD) — this file is the single source of truth for all product requirements, scope, and standards  
 **Last Updated**: 2026-03-28  
 **Status**: ? Active — Phase 1 MVP