docs(deploy): document PV/UV stats and real client IP via nginx realip

deploy/nginx/update-cloudflare-ips.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+# 生成 Cloudflare 节点网段清单，供 realip-cloudflare.conf 使用。
+#
+# 用法: sudo bash deploy/nginx/update-cloudflare-ips.sh [输出文件]
+# 默认输出: /etc/nginx/cloudflare-ips.conf
+set -euo pipefail
+
+OUT="${1:-/etc/nginx/cloudflare-ips.conf}"
+
+{
+  for url in https://www.cloudflare.com/ips-v4 https://www.cloudflare.com/ips-v6; do
+    curl -fsSL "$url" | sed '/^[[:space:]]*$/d; s/^/set_real_ip_from /; s/$/;/'
+  done
+} > "${OUT}.tmp"
+
+mv "${OUT}.tmp" "$OUT"
+echo "已写入 $OUT"
+
+if command -v nginx >/dev/null 2>&1; then
+  nginx -t && nginx -s reload
+fi