Unset TRUSTED_PROXIES trusts the RFC 1918 ranges (closes #119)

With TRUSTED_PROXIES unset, bin/entrypoint.sh gives nginx one
set_real_ip_from line for each of 10.0.0.0/8, 172.16.0.0/12 and
192.168.0.0/16, as sneak ruled on 2026-09-22 for every app. A list
replaces them, and set and empty trusts no proxy; each entry is checked
as before. The backend inside the container still trusts only
127.0.0.1/32. README.md, configs/nginx.conf and the comment in
script/frontend-viewport-test say the new default.

Model: opus-5-5

configs/nginx.conf

@@ -18,9 +18,10 @@ server {
 
     # The client address comes from X-Forwarded-For only on a request
     # from the reverse proxies in TRUSTED_PROXIES: bin/entrypoint.sh
-    # writes one set_real_ip_from line for each into this file, and
-    # leaves it empty when TRUSTED_PROXIES is unset, so that by default
-    # the client address is the one each request comes from.
+    # writes one set_real_ip_from line for each into this file. Unset,
+    # TRUSTED_PROXIES is the three private ranges of RFC 1918; set and
+    # empty, the file is empty and the client address is the one each
+    # request comes from.
     include /etc/nginx/trusted-proxies.conf;
     real_ip_header X-Forwarded-For;
     real_ip_recursive on;