feat: 扩展发布打包支持多组件多架构多格式产物

- 新增 web 组件独立发布为 nex-web_<version>.tar.gz
- server 新增 arm64 架构、macOS universal、Windows arm64 产物
- desktop 新增 arm64 架构支持（Linux/Windows）
- Linux desktop 新增 AppImage、deb、rpm 安装包格式
- macOS desktop 新增 unsigned DMG 安装包
- 统一发布资产命名为 {component}_{version}_{platform}_{arch}.{ext}
- 新增 SHA256SUMS 校验和清单覆盖全部发布资产
- versionctl 新增 asset-name CLI 支持按参数生成资产文件名
- Makefile release target 重构为组件/平台/架构参数化
- GitHub Actions release workflow 扩展多组件多架构构建矩阵
- 同步更新 openspec 主规范（desktop-app/release-pipeline/workspace-command-flows）

packaging/linux/AppRun

@@ -0,0 +1,5 @@
+#!/bin/sh
+set -eu
+
+APPDIR=$(dirname "$(readlink -f "$0")")
+exec "$APPDIR/usr/bin/nex" "$@"

packaging/linux/nex.desktop

@@ -0,0 +1,9 @@
+[Desktop Entry]
+Type=Application
+Name=Nex
+Comment=AI Gateway
+Exec=nex
+Icon=nex
+Terminal=false
+Categories=Development;Network;
+StartupNotify=false

packaging/linux/nex.spec

@@ -0,0 +1,29 @@
+Name: nex
+Version: %{nex_version}
+Release: 1%{?dist}
+Summary: AI Gateway desktop application
+License: Apache-2.0
+URL: https://github.com/nex/gateway
+Requires: gtk3
+Requires: libayatana-appindicator-gtk3
+Requires: xdg-utils
+
+%description
+Nex is an AI Gateway desktop application.
+
+%prep
+
+%build
+
+%install
+mkdir -p %{buildroot}/usr/bin
+install -m 0755 %{nex_binary} %{buildroot}/usr/bin/nex
+mkdir -p %{buildroot}/usr/share/applications
+install -m 0644 %{nex_desktop_file} %{buildroot}/usr/share/applications/nex.desktop
+mkdir -p %{buildroot}/usr/share/icons/hicolor
+cp -a %{nex_icons_dir}/. %{buildroot}/usr/share/icons/hicolor/
+
+%files
+/usr/bin/nex
+/usr/share/applications/nex.desktop
+/usr/share/icons/hicolor/*/apps/nex.png