fix(security): remediate 2026-05-12 audit findings (Stages 2–5)

Remediation of the 2026-05-12/13 audits (78 findings + cluster gaps),
tracked in deploy-k3s/SECURITY.md, plus fixes from two independent
post-remediation reviews.

Auth & sessions:
- SHA-256 hashed auth-token storage (C1); prior-token cache eviction on
  re-login (MEDIUM-1)
- local Google JWKS verification, iss/aud/exp checks (C2/C3)
- constant-time login + generic errors (L1/LIVE-L11/LIVE-L13)
- per-account login lockout keyed on distinct source IPs (M5/MEDIUM-3)
- verified-email gating, login rate limiting (LIVE-L19, H1-H3)

IAP & webhooks:
- Apple/Google cross-account replay protection (C5/C6/C10/C13, H5/H6)
- migrations 000003-000006 (token hashing, IAP replay, audit_log +
  webhook_event_log table creation, append-only audit log)

Authorization & races:
- file-ownership owner-OR-member fix (C7), atomic share-code join
  (C9/H9), device-token reassignment (C8/LOW-3)

Secrets & deploy:
- secrets file-mounted at /etc/honeydue/secrets, not env (F8); Redis
  password out of the ConfigMap (HIGH-1); B2 keys reconciled
- digest-pinned images, admin ingress hardening, CSP/HSTS, /metrics
  lockdown; kubeconfig 0600, etcd secrets-encryption, fail2ban +
  unattended-upgrades at provision; secret-rotation runbook

Build, vet, and the full test suite (incl. -race) pass; the goose
migration chain is verified against PostgreSQL 16.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/deployment/06-traefik-ingress.md

@@ -1,5 +1,13 @@
 # 06 — Traefik Ingress
 
+> **Updated 2026-05-15 (security remediation):** the Traefik middleware set
+> changed — `cloudflare-only` + `admin-auth` are now attached to the admin
+> ingress, a strict `auth-rate-limit` middleware fronts the auth endpoints
+> (via a dedicated `honeydue-api-auth` Ingress), and `security-headers`
+> gained COOP/CORP + a 2-year preload HSTS and dropped the deprecated
+> `X-XSS-Protection`. `deploy-k3s/SECURITY.md` is the authoritative
+> current-state record.
+
 ## Summary
 
 Traefik is the reverse proxy that routes external HTTP requests to the