feat: per-forward worker 模型 — 每条转发独立 frpc 配置+独立进程

核心改动（ring 协议不变，Task 本来就是 {Local,Remote,Link} 三元组）:
- process.WorkerKey: worker 键改为 'local~remote~port' 三元组
- renderForward: 每条 forward 渲染只含 1 个 proxy 的独立 frpc 配置
  (替代 renderRemote 把该 remote 全部 forwards 塞进一个进程)
- ClaimFn/RevokeFn: 认领/撤销只操作这一条 forward 自己的进程
- SyncWorkers/auto-start: 只拉起 localOnly 转发的独立进程,
  集群转发由 ring 认领节点拉起 (消除三台争抢 proxy already exists)
- RemoteStatus/StartRemote/StopRemote/RestartRemote: remote 级聚合辅助,
  保持 /profiles API 形状不变, 前端零改动
- handleStatus/logs: 按 worker key 解析真实 remote 名

效果: 三台节点的 frpc 各自只注册自己拥有的 proxy, 单条转发故障不再波及兄弟

internal/process/worker_key.go

@@ -0,0 +1,39 @@
+package process
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// WorkerKey is the unique identity of ONE forward's worker process:
+//
+//	"<local>~<remote>~<port>"
+//
+// The per-forward worker model gives every link its own frpc process, config
+// file and log file. This fixes the multi-node proxy-name fight of the old
+// per-remote model (every node rendered the SAME proxy list and raced to
+// register them on frps -> "proxy already exists"), and isolates faults: one
+// crashing forward can no longer take its siblings down.
+//
+// '~' is a legal filename character on every supported OS (including Windows,
+// unlike ':') and is rare in user-chosen node names. ParseWorkerKey rejects
+// malformed keys so callers fail loudly instead of silently mis-rendering.
+func WorkerKey(local, remote string, port int) string {
+	return fmt.Sprintf("%s~%s~%d", local, remote, port)
+}
+
+// ParseWorkerKey splits a worker key back into its (local, remote, port)
+// forward triple. ok=false for anything that is not a well-formed key
+// (e.g. legacy per-remote worker names).
+func ParseWorkerKey(key string) (local, remote string, port int, ok bool) {
+	parts := strings.Split(key, "~")
+	if len(parts) != 3 {
+		return "", "", 0, false
+	}
+	p, err := strconv.Atoi(parts[2])
+	if err != nil || parts[0] == "" || parts[1] == "" || p <= 0 {
+		return "", "", 0, false
+	}
+	return parts[0], parts[1], p, true
+}