[ci skip] Infrastructure hardening: security, monitoring, reliability, maintainability

Phase 1 - Critical Security:
- Netbox: move hardcoded DB/superuser passwords to variables
- MeshCentral: disable public registration, add Authentik auth
- Traefik: disable insecure API dashboard (api.insecure=false)
- Traefik: configure forwarded headers with Cloudflare trusted IPs

Phase 2 - Security Hardening:
- Add security headers middleware (HSTS, X-Frame-Options, nosniff, etc.)
- Add Kyverno pod security policies in audit mode (privileged, host
  namespaces, SYS_ADMIN, trusted registries)
- Tighten rate limiting (avg=10, burst=50)
- Add Authentik protection to grampsweb

Phase 3 - Monitoring & Alerting:
- Add critical service alerts (PostgreSQL, MySQL, Redis, Headscale,
  Authentik, Loki)
- Increase Loki retention from 7 to 30 days (720h)
- Add predictive PV filling alert (predict_linear)
- Re-enable Hackmd and Privatebin down alerts

Phase 4 - Reliability:
- Add resource requests/limits to Redis, DBaaS, Technitium, Headscale,
  Vaultwarden, Uptime Kuma
- Increase Alloy DaemonSet memory to 512Mi/1Gi

Phase 6 - Maintainability:
- Extract duplicated tiers locals to terragrunt.hcl generate block
  (removed from 67 stacks)
- Replace hardcoded NFS IP 10.0.10.15 with var.nfs_server (114
  instances across 63 files)
- Replace hardcoded Redis/PostgreSQL/MySQL/Ollama/mail host references
  with variables across ~35 stacks
- Migrate xray raw ingress resources to ingress_factory modules

stacks/nextcloud/chart_values.yaml

@@ -28,13 +28,13 @@ nextcloud:
 
 externalRedis:
   enabled: true
-  host: redis.redis.svc.cluster.local
+  host: ${redis_host}
 
 # Currently not in use; we use the nextcloud.db sqlite3
 externalDatabase:
   enabled: false
   type: mysql
-  host: mysql.dbaas.svc.cluster.local
+  host: ${mysql_host}
   user: nextcloud
   password: ${db_password}
   databse: nextcloud