fix(caddy,authentik): auth guarded vhosts by proxying the whole request through authentik

The forward_auth target /outpost.goauthentik.io/auth/caddy does not exist
in authentik 2026.8 (verified live: 404 for every header combination; the
URL tree has no outpost auth prefix at all — the outpost worker dials back
to core over ws/outpost/<uuid>/ instead). Unauthenticated subrequests got
404, Caddy treated >=400 as 'not authenticated' and redirected browsers to
the dead path — users saw authentik's own Not-Found page.

Fix: guarded vhosts now proxy the whole request through authentik-server:9000
with X-authentik-meta-outpost/-provider/-app headers (the exact header set
this build's Traefik controller emits, adapted for Caddy). Unauthenticated
clients get the login flow served in place; once a session exists,
authentik proxies on to the provider's internal_host — now
http://caddy:8017, a new post-auth internal listener that routes straight to
the app. The chain terminates; nothing dials back into authentik.

Live DB changes applied alongside (postgres is the source of truth):
provider pk=1 authentication_flow=default-authentication-flow (was NULL —
the actual cause of the 404s) and internal_host=http://caddy:8017 (was
self-referential http://authentik-server:9000).

tests/caddyfile.bats

@@ -125,10 +125,11 @@ CADDYFILE="$REPO_ROOT/dankclaw/Caddyfile"
     # franksdank.casa is not in the same Porkbun account, so it cannot get
     # a DNS-01 Let's Encrypt cert; it stays explicitly http. Every other
     # client-facing site address must carry no http:// prefix. The internal
-    # listener (http://:8016) is not client-facing — Anubis dials it over
-    # container DNS after verifying a client, so plain HTTP is intended.
+    # listeners (http://:8016, http://:8017) are not client-facing — Anubis
+    # and Authentik dial them over container DNS after verifying a client,
+    # so plain HTTP is intended.
     local offenders
-    offenders=$(grep -E '^http://' "$CADDYFILE" | grep -v 'plex\.franksdank\.casa' | grep -v '^http://:8016' || true)
+    offenders=$(grep -E '^http://' "$CADDYFILE" | grep -v 'plex\.franksdank\.casa' | grep -vE '^http://:801[67]' || true)
     [ -z "$offenders" ] || { echo "non-.casa http:// vhosts: $offenders"; return 1; }
 }