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>

go.mod

@@ -27,10 +27,10 @@ require (
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.43.0
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.43.0
 	go.opentelemetry.io/otel/sdk v1.43.0
-	golang.org/x/crypto v0.49.0
+	golang.org/x/crypto v0.51.0
 	golang.org/x/oauth2 v0.35.0
-	golang.org/x/term v0.41.0
-	golang.org/x/text v0.35.0
+	golang.org/x/term v0.43.0
+	golang.org/x/text v0.37.0
 	golang.org/x/time v0.15.0
 	google.golang.org/api v0.257.0
 	gopkg.in/yaml.v3 v3.0.1
@@ -117,9 +117,9 @@ require (
 	go.opentelemetry.io/otel v1.43.0
 	go.opentelemetry.io/otel/metric v1.43.0 // indirect
 	go.opentelemetry.io/otel/trace v1.43.0
-	golang.org/x/net v0.52.0 // indirect
-	golang.org/x/sync v0.20.0 // indirect
-	golang.org/x/sys v0.42.0 // indirect
+	golang.org/x/net v0.53.0 // indirect
+	golang.org/x/sync v0.20.0
+	golang.org/x/sys v0.44.0 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20260401024825-9d38bb4040a9 // indirect
 	google.golang.org/grpc v1.80.0 // indirect
 	google.golang.org/protobuf v1.36.11 // indirect