feat(nginx): render-nginx.sh + www->apex redirect vhost

Add tooling/render-nginx.sh: pulls BASE_DOMAIN/CADDY_HTTP_PORT from .env,
defaults APP_DIR to the repo checkout, renders a vhost template (default the
caddy-front one) to stdout, or --install writes + symlinks + nginx -t + reloads.
Document it in the README, replacing the manual envsubst one-liner.

Also add the www.${BASE_DOMAIN} canonical 301->apex block and put www in the
LE_SUBDOMAINS default so its cert is issued.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tooling/issue-letsencrypt.sh

@@ -17,7 +17,7 @@
 #   OVH_CK            OVH consumer key (obtained on first run — see below)
 #   OVH_END_POINT     OVH API endpoint (e.g. ovh-eu)
 # optional:
-#   LE_SUBDOMAINS     space-separated (default: "auth pack distribution")
+#   LE_SUBDOMAINS     space-separated (default: "auth pack distribution www")
 #   LE_STAGING=1      use the LE staging CA (untrusted, for dry runs)
 #
 # First-time OVH consumer key: set OVH_AK/OVH_AS/OVH_END_POINT, leave OVH_CK
@@ -53,7 +53,7 @@ ACME="${ACME_SH:-$HOME/.acme.sh/acme.sh}"
 then re-run (or set ACME_SH=/path/to/acme.sh)."
 
 CERT_DIR="${CERT_DIR:-certs}"
-read -r -a SUBDOMAINS <<< "${LE_SUBDOMAINS:-auth pack distribution}"
+read -r -a SUBDOMAINS <<< "${LE_SUBDOMAINS:-auth pack distribution www}"
 
 if [ "${LE_STAGING:-0}" = "1" ]; then
   SERVER="letsencrypt_test"; warn "STAGING mode — certs will NOT be trusted by browsers"