docs: add end-to-end walkthrough guide

[Taure]

Summary

Adds guides/walkthrough.md — a worked example showing how to audit a Nova web app end-to-end.

What it covers

• Project setup + sys.config for both adapters
• Applying the Kura schema + hardening_sql/0 (REVOKE UPDATE/DELETE)
• Actor extraction helper from nova_auth sessions
• A pre_http_request plugin that generates/echoes X-Request-Id
• Login handler — log_async on success, log on failure (security-sensitive)
• Upload handler with nova_storage integration
• Admin delete handler with the sync-log-before-destructive pattern
• GDPR right-of-access query helper (cursor-paginated)
• Admin reporting query
• Incident-response trace by request_id
• Liveboard / Arizona view sketch
• Overflow alerting via telemetry
• Explicit "what we did NOT do" — retention, PII detection, tamper-evidence, cross-service correlation

Why concrete code?

User feedback: a single high-quality walkthrough teaches more than four small abstract guides. Every block is paste-ready Erlang.

Test plan

• CI green (docs-only PR, paths-ignore should skip CI; release workflow is docs-only too)
• Verify ex_doc picks up the new guide in the 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