docs: add service README.md files + update AGENTS.md decisions

- Create README.md for 25+ service modules with container info, API surface, storage
- Document attestor-tileproxy separation rationale (air-gap network isolation)
- Document opsmemory-advisoryai separation rationale (resource isolation, blast radius)
- Update Timeline AGENTS.md with merged indexer info

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/Integrations/README.md

@@ -0,0 +1,17 @@
+# Integrations
+
+**Container(s):** stellaops-integrations-web
+**Slot:** 42  |  **Port:** 8080  |  **Consumer Group:** integrations
+**Resource Tier:** light
+
+## Purpose
+The Integrations service provides a unified catalog and management API for external tool connections. It supports plugins for GitHub App, Harbor, Gitea, Jenkins, Nexus, Docker Registry, GitLab, Vault, Consul, and eBPF Agent integrations. It includes AI Code Guard capabilities and manages authentication references (AuthRef) for secure credential resolution.
+
+## API Surface
+- `integrations` (via Router) — integration catalog CRUD, connection testing, credential management (AuthRef/Vault), AI Code Guard endpoints, plugin discovery
+
+## Storage
+PostgreSQL (via `ConnectionStrings:IntegrationsDb`); EF Core with auto-migrations (`AddStartupMigrations`)
+
+## Background Workers
+None