Harden installer: slow-mirror fallback, arg-preserving sudo, safer preflight

[fengren]

Summary

• Preserve CLI args across the sudo re-exec so options like -y/--dir are no longer dropped
• Fall back GitHub → Gitee on slow/failed downloads and on version-resolution API failures
• Validate HTTPS/Admin/SMTP ports; skip forced port shift on reruns of an existing install
• Report available (not total) memory on Linux (MemAvailable) and macOS (vm_stat)
• Detect install domain via the default-route interface instead of hostname -I (avoids docker0/veth)
• Merge duplicate GitHub reachability probes; quiet success-path logging
• Optional SHA256SUMS integrity verification for downloaded release files
• Exponential backoff for docker compose up retries

Test plan

• bash -n install.sh
• scripts/test-install.sh (all platform smoke tests pass on macOS)
• Remote regression on Ubuntu 24.04: fresh config download + rerun over an existing v1.3.0 install; health check passed, stack healthy

Closes #36

Made with Orca 🐋

[fengren]

实现总结

• 核心变更：修复 sudo 重执行丢失 CLI 参数；GitHub 慢/失败时自动降级 gitee（含版本解析）
• 核心变更：HTTPS/Admin/SMTP 端口校验，rerun 时不再误迁移已占用端口
• 核心变更：Linux/macOS 改用可用内存检测；域名探测走默认路由接口
• 核心变更：可选 SHA256SUMS 校验、指数退避重试、合并重复网络探测
• 验证：本地 smoke 全绿 + Ubuntu 24.04 远程 rerun 回归通过
• PR: Harden installer: slow-mirror fallback, arg-preserving sudo, safer preflight #36
• Commit: 17d7402