docs: add operations runbook

[Taure]

Summary

Adds guides/runbook.md — concrete operations playbook for nova_audit deployments.

Contents

• Quick reference table (symptom → first action)
• 4 mandatory alerts with attach code (overflow, write errors, hardening drift, write latency)
• Dashboard SQL (events/sec, top actions, failed events)
• Overflow triage: escalating fix list (raise max_queue → shigoto → sync mode → audit upstream throughput)
• Write-error reasons + fixes table
• Slow-query triage
• Retention pattern: monthly partitions + S3 Object Lock archival via a dedicated DELETE-privileged role
• Retention windows reference (GDPR / DORA / NIS2 / AI Act / SOX)
• Compliance export SQL (GDPR Art 15, annual audit, privileged access review)
• Tamper investigation procedure
• Capacity sizing (event throughput, on-disk size, partition thresholds)
• Backup + restore with WORM storage
• Additive-only schema migration rules
• On-call response sequence

Test plan

• CI green (markdown + rebar.config ex_doc list update)
• ex_doc picks up the new guide in navigation

[github-actions]

ℹ️ 15 OTP CVEs auto-ignored (already fixed in running version)

These CVEs are patched in the installed OTP version but NVD data
has not been updated to reflect this. They are excluded from the
scan via an auto-generated .trivyignore.

CVE	Details
CVE-2026-32147	Fixed in 28.4.3, running 28.5 — Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') in SFTP chroot
CVE-2026-28808	Fixed in 28.4.2, running 28.5 — ScriptAlias CGI targets bypass directory auth (mod_auth vs mod_cgi path mismatch)
CVE-2026-32144	Fixed in 28.4.2, running 28.5 — OCSP designated-responder authorization bypass — missing signature verification (RFC 6960 §4.2.2.2)
CVE-2026-28810	Fixed in 28.4.2, running 28.5 — Predictable DNS Transaction IDs Enable Cache Poisoning in Built-in Resolver
CVE-2026-23943	Fixed in 28.4.1, running 28.5 — Pre-auth SSH DoS via unbounded zlib inflate
CVE-2026-23942	Fixed in 28.4.1, running 28.5 — SFTP root escape via component-agnostic prefix check in ssh_sftpd
CVE-2026-23941	Fixed in 28.4.1, running 28.5 — Request smuggling via first-wins Content-Length parsing in inets httpd
CVE-2026-21620	Fixed in 28.3.2, running 28.5 — TFTP Path Traversal
CVE-2016-1000107	Fixed in 28.0.4, running 28.5 — Httpd CGI Scripts Environment Variable Pollution AKA "httpoxy"
CVE-2025-58050	Fixed in 28.0.3, running 28.5 — Buffer Read Overflow on Regular Expressions with (*scs:) and (*ACCEPT)
CVE-2025-48038	Fixed in 28.0.3, running 28.5 — SSH Unverified File Handles can Cause Excessive Use of System Resources
CVE-2025-48039	Fixed in 28.0.3, running 28.5 — SSH Unverified Paths can Cause Excessive Use of System Resources
CVE-2025-48040	Fixed in 28.0.3, running 28.5 — SSH Malicious Key Exchange Messages may Lead to Excessive Resource Consumption
CVE-2025-48041	Fixed in 28.0.3, running 28.5 — SSH_FXP_OPENDIR may Lead to Exhaustion of File Handles
CVE-2025-4748	Fixed in 28.0.1, running 28.5 — Absolute Path in Zip Module