feat: 原生安装包 — deb/rpm/systemd + NSIS setup.exe + macOS pkg

此前交付的 tar.gz/zip 仅是解压直用包，补齐真正的平台安装包：
- Linux: .deb (dpkg-deb) 与 .rpm (rpmbuild)，装 systemd 单元 + 专用
  系统账号 + /etc/webui4frpc 配置，非 root 运行 + 加固
- Windows: NSIS setup.exe，向导收集监听地址/凭据，注册卸载器 +
  防火墙放行（amd64/arm64）
- macOS: .pkg（在 Linux 上手工 xar+mkbom 组装 flat package），launchd
  开机自启 + env 配置文件（amd64/arm64）
- scripts/release.sh 纳入 build_installers.sh 阶段；README 增「安装」
  章节逐平台说明

已知限制：rpmbuild 无法在非 RHEL 主机交叉构建 aarch64（Debian rpm
只有 x86_64 构建 arch），aarch64 rpm 需在原生 ARM 机器构建；Linux/ARM
场景已由 deb-arm64 覆盖。

packaging/common/LICENSE.txt

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 JianFeeeee
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

packaging/common/webui4frpc.env

@@ -0,0 +1,8 @@
+# webui4frpc runtime configuration
+# 默认监听全部接口的 7500 端口；请修改密码后再投入生产。
+W4F_ADDR=0.0.0.0:7500
+W4F_USER=admin
+W4F_PASSWORD=admin
+
+# 可选：首次提供的 frpc 二进制路径（留空则从 Web UI 手动/自动安装）
+# W4F_FRPC=/usr/local/bin/frpc

packaging/common/webui4frpc.service

@@ -0,0 +1,25 @@
+[Unit]
+Description=webui4frpc - visual frpc controller (cluster node)
+Documentation=https://gitcode.com/JianFeeeee/webui4frpc
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+User=webui4frpc
+Group=webui4frpc
+EnvironmentFile=/etc/webui4frpc/webui4frpc.env
+ExecStart=/usr/bin/webui4frpc -addr ${W4F_ADDR} -user ${W4F_USER} -password ${W4F_PASSWORD} -workdir /var/lib/webui4frpc
+Restart=always
+RestartSec=5
+LimitNOFILE=65535
+
+# hardening
+NoNewPrivileges=true
+PrivateTmp=true
+ProtectSystem=full
+ProtectHome=true
+ReadWritePaths=/var/lib/webui4frpc
+
+[Install]
+WantedBy=multi-user.target