webui4frpc: 独立可用的可视化 frpc 控制器 (M0)

- 零 frp 源码依赖，单二进制 (Go + Vue3 + VueFlow + Element Plus)
- 画布多对多连线，渲染 tcp/udp/http/https frpc 配置
- worker 进程管理：自愈、日志轮转、崩溃退避重启
- frpc 一键安装 (GitHub Releases) + 手动指定路径
- 三页 UI：状态(默认)/连接配置/设置
- 状态页实时节点/转发状态，节点可增删改启停
- 画布冲突检查：端口/域名冲突标红 + 弹窗拦截保存
- backend 单测覆盖 store/render/process/httpapi/install
- plan.md + FRPC_FEATURES_AUDIT.md 文档

internal/process/process_unix.go

@@ -0,0 +1,21 @@
+//go:build !windows
+
+package process
+
+import (
+	"os/exec"
+	"syscall"
+)
+
+// setSysProcAttr runs the worker in its own process group.
+func setSysProcAttr(cmd *exec.Cmd) {
+	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+}
+
+// signalGroup delivers sig to the worker and its whole process group.
+func signalGroup(cmd *exec.Cmd, sig syscall.Signal) {
+	if cmd.Process == nil {
+		return
+	}
+	_ = syscall.Kill(-cmd.Process.Pid, sig)
+}