Authentik SSO + homepage naked domain

Auth layer (Authentik 2026.8.0):
- compose: 3-service stack (authentik-postgres, authentik-server, authentik-worker),
  postgres health-gated, bind mounts under /home/dank/authentik
- Caddyfile: auth.franksdank.cloud vhost; forward_auth on the no-auth vhosts
  (homepage, SearXNG, Hermes, Prometheus, RomM, Copyparty); outpost path
  proxied first in a route block
- .env.example: AUTHENTIK_PG_PASS + AUTHENTIK_SECRET_KEY
- deploy.sh: render only CADDY_BASICAUTH_HASH (the homepage per-user hashes
  are retired; grafana + pihole keep basicauth)
- tests/authentik.bats (new) + updated homepage/caddyfile/pihole seams
- docs: Authentik.md + per-service pages; Caddy.md + Homepage.md updated

Homepage (naked domain):
- Caddyfile: dankclaw.franksdank.cloud -> franksdank.cloud www.franksdank.cloud;
  dankclaw + dankserver redirect to it; bare-IP catch-all updated
- addn-hosts: A records for the naked domain, www, and auth (all -> 143)
- tests/pihole.bats: vhost_names handles multi-address blocks; TLD check
  allows the naked domain

All 146 tests pass.

docs/index.md

@@ -65,6 +65,10 @@ covers both workloads).
 - [[LAN-DNS]] — name resolution, Pi-hole, router DNS hand-off
 - [[Pi-hole]] — the LAN DNS server (quadlet, records, web UI)
 - [[Caddy]] — reverse proxy and TLS
+- [[Authentik]] — the homelab's SSO / OIDC provider (forward_auth)
+- [[authentik-postgres]] — Authentik database service
+- [[authentik-server]] — Authentik server + Caddy outpost service
+- [[authentik-worker]] — Authentik background worker service
 - [[Homepage]] — password-protected service index
 - [[Homepage Design Grilling]] — homepage decision log and open questions
 - [[Observability]] — Grafana, Prometheus, Loki, Alloy