nginx: trust X-Forwarded-For only from TRUSTED_PROXIES (closes #64)

nginx trusted X-Forwarded-For from every RFC1918 address, so a client
reaching it from one could write a new address on each request and
get a fresh rate-limit allowance. The container's TRUSTED_PROXIES now
names the reverse proxies nginx trusts, none by default.
bin/entrypoint.sh makes each entry a CIDR, checks it with the new
"netwatch-server check-cidr", which runs the server's own
TRUSTED_PROXIES parsing, and writes one set_real_ip_from line per
entry into /etc/nginx/trusted-proxies.conf, which nginx.conf includes.
The backend is started with TRUSTED_PROXIES=127.0.0.1/32, since nginx
is its only client. The viewport test mounts an empty file there.

Model: opus-5-5

backend/internal/middleware/export_test.go

@@ -29,7 +29,3 @@ func ClientIP(
 ) string {
 	return clientIP(remoteAddr, header, trusted)
 }
-
-func ParseTrustedProxies(cidrs []string) ([]netip.Prefix, error) {
-	return parseTrustedProxies(cidrs)
-}