feat(rank6): node-exporter renders from a template; guard chain is one snippet

- service-map render node-exporter-unit --host H: the MIRROR pair comment
  ('keep this file in step') becomes a template. Per-host title, LAN
  address from the hosts map, port from the node-<host> scrape job. Both
  tracked quadlets are now rendered artifacts; check_drift gates them.
- dankclaw/Caddyfile: the nine verbatim Anubis pre-auth chains
  (reverse_proxy anubis:8923 + X-Real-Ip) collapse into the (guarded)
  named snippet; guarded vhosts are 'import guarded'. Validated with real
  caddy 2.11.7 (import resolution clean; the stock image stops at the
  porkbun module and the git basicauth placeholder, as designed).
- vhost-scoped guard greps (authentik, homepage_caddy, marreta_quadlet)
  now pin 'import guarded' in the vhost block.
- Service Inventory + Authentik docs carry the new laws.

tests/caddyfile.bats

@@ -251,3 +251,14 @@ CADDYFILE="$REPO_ROOT/dankclaw/Caddyfile"
     grep -q -- '--server.http.listen-addr=0.0.0.0:12345' "$unit"
     grep -q '^PublishPort=127.0.0.1:12345:12345$' "$unit"
 }
+
+@test "the guard chain is a named snippet the guarded vhosts import" {
+    # Rank 6: the Anubis pre-auth chain (reverse_proxy anubis:8923 with the
+    # X-Real-Ip header_up) existed as nine verbatim copies. One snippet,
+    # per-vhost imports; a chain edit is a one-line change.
+    grep -q '^(guarded) {' "$CADDYFILE"
+    local imports
+    imports=$(grep -c $'^\timport guarded$' "$CADDYFILE")
+    [ "$imports" -ge 9 ]
+    [ "$(grep -c 'reverse_proxy anubis:8923' "$CADDYFILE")" -eq 1 ]
+}