新增：SFTP直连+连接池+autoConnect+文件服务器端口自动回退

- SFTP模块：连接/断开/文件CRUD/系统信息采集/base64二进制写入
- 连接池：多服务器同时在线，瞬间切换profile
- autoConnect：启动时自动连接所有非本地服务器
- 端口自动回退：listenWithFallback消除TOCTOU，解决端口冲突崩溃
- 文件服务器URL集中管理：file-server.ts消除8+处硬编码端口
- Sidebar设置面板：添加服务器/自动连接/自动刷新开关
- 修复：validateFilePath越界panic、正则预编译
- 修复：注释准确性（RemoveAll/端口8073/动态端口文档）

internal/agent/handler/server_handler.go

@@ -46,8 +46,8 @@ func (h *Handler) HTMLPreviewProxy(c echo.Context) error {
 	}
 	theme := c.QueryParam("theme")
 
-	targetURL := fmt.Sprintf("http://localhost:8073/localfs/html-preview?path=%s&theme=%s",
-		url.QueryEscape(clean), url.QueryEscape(theme))
+	targetURL := fmt.Sprintf("%s/localfs/html-preview?path=%s&theme=%s",
+		h.cfg.FileServerAddr(), url.QueryEscape(clean), url.QueryEscape(theme))
 
 	resp, err := http.Get(targetURL)
 	if err != nil {

internal/agent/handler/system_handler.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"fmt"
 	"net/http"
 	"os"
 	"runtime"
@@ -9,6 +10,9 @@ import (
 	"u-desk/internal/agent/model"
 
 	"github.com/labstack/echo/v4"
+	"github.com/shirou/gopsutil/v3/cpu"
+	"github.com/shirou/gopsutil/v3/disk"
+	"github.com/shirou/gopsutil/v3/mem"
 )
 
 // Ping 健康检查
@@ -111,3 +115,39 @@ func (h *Handler) Drives(c echo.Context) error {
 
 	return c.JSON(http.StatusOK, model.OK(drives))
 }
+
+// Stats 返回系统资源使用统计（CPU/内存/磁盘）
+func (h *Handler) Stats(c echo.Context) error {
+	info := make(map[string]interface{})
+
+	// CPU
+	if cores, err := cpu.Counts(true); err == nil {
+		info["cpu_cores"] = cores
+	}
+	if percents, err := cpu.Percent(0, false); err == nil && len(percents) > 0 {
+		info["cpu_usage"] = fmt.Sprintf("%.0f%%", percents[0])
+	}
+
+	// 内存
+	if memInfo, err := mem.VirtualMemory(); err == nil {
+		info["mem_total"] = memInfo.Total
+		info["mem_used"] = memInfo.Used
+		info["mem_usage"] = fmt.Sprintf("%.0f%%", memInfo.UsedPercent)
+	}
+
+	// 磁盘（取根分区）
+	if partitions, err := disk.Partitions(false); err == nil {
+		for _, p := range partitions {
+			if p.Mountpoint == "/" || (runtime.GOOS == "windows" && len(p.Mountpoint) == 3 && p.Mountpoint[1] == ':') {
+				if usage, err := disk.Usage(p.Mountpoint); err == nil {
+					info["disk_total"] = usage.Total
+					info["disk_used"] = usage.Used
+					info["disk_usage"] = fmt.Sprintf("%.0f%%", usage.UsedPercent)
+				}
+				break
+			}
+		}
+	}
+
+	return c.JSON(http.StatusOK, model.OK(info))
+}