优化：工具栏高度对齐+面板统一+远程连接架构+自动恢复预览

- 工具栏：面包屑与右侧组件像素级等高(:deep 34px)、合并重复search handler、统一分隔符样式、删除死代码
- 面板对齐：三面板header统一padding/font-size、文件列表分页固定底部(自定义紧凑)、表头默认隐藏、滚动条统一样式
- 预览区：始终显示空白预览面板、重启自动恢复上次打开文件
- 收藏夹：简化计数显示(共N项)
- 远程连接：ConnectionIndicator自适应UI(无远程显示mini云图标)、ConnectionDialog支持编辑配置、transport抽象层(本地Wails/远程HTTP双模式)、agent后端模块

internal/agent/handler/file_handler.go

@@ -0,0 +1,176 @@
+package handler
+
+import (
+	"net/http"
+	"path/filepath"
+	"strings"
+
+	"u-desk/internal/agent/model"
+	"u-desk/internal/filesystem"
+
+	"github.com/labstack/echo/v4"
+)
+
+type writeFileReq struct {
+	Content string `json:"content"`
+}
+
+type createReq struct {
+	Type string `json:"type"` // "file" or "dir"
+	Name string `json:"name"`
+}
+
+type renameReq struct {
+	NewPath string `json:"new_path"`
+}
+
+type uploadReq struct {
+	Content string `json:"content"` // base64 编码内容
+}
+
+// ListOrStat 列出目录或获取文件信息（?get=stat 时返回单文件信息）
+func (h *Handler) ListOrStat(c echo.Context) error {
+	path := getPath(c)
+	action := c.QueryParam("get")
+
+	if action == "stat" {
+		info, err := h.fsSvc.GetFileInfo(path)
+		if err != nil {
+			return c.JSON(http.StatusOK, model.NotFound(err.Error()))
+		}
+		return c.JSON(http.StatusOK, model.OK(info))
+	}
+
+	files, err := h.fsSvc.ListDir(path)
+	if err != nil {
+		return c.JSON(http.StatusOK, model.InternalError(err.Error()))
+	}
+	// 限制返回数量，避免大目录导致前端卡顿
+	limit := c.QueryParam("limit")
+	if limit != "" {
+		n := 0
+		for i, f := range files {
+			if n >= 500 { // 硬限制 500 条
+				break
+			}
+			files[i] = f
+			n++
+		}
+		files = files[:n]
+	}
+	return c.JSON(http.StatusOK, model.OK(files))
+}
+
+// ReadFile 读取文件文本内容
+func (h *Handler) ReadFile(c echo.Context) error {
+	path := getPath(c)
+	content, err := h.fsSvc.ReadFile(path)
+	if err != nil {
+		return c.JSON(http.StatusOK, model.InternalError(err.Error()))
+	}
+	return c.JSON(http.StatusOK, model.OK(map[string]string{
+		"content": content,
+	}))
+}
+
+// WriteFile 写入文件文本内容
+func (h *Handler) WriteFile(c echo.Context) error {
+	path := getPath(c)
+	var req writeFileReq
+	if err := c.Bind(&req); err != nil {
+		return c.JSON(http.StatusBadRequest, model.BadRequest("无效请求体"))
+	}
+	if err := h.fsSvc.WriteFile(path, req.Content); err != nil {
+		return c.JSON(http.StatusInternalServerError, model.InternalError(err.Error()))
+	}
+	return c.JSON(http.StatusOK, model.NoContent())
+}
+
+// Create 创建文件或目录
+func (h *Handler) Create(c echo.Context) error {
+	parentPath := getPath(c)
+	var req createReq
+	if err := c.Bind(&req); err != nil {
+		return c.JSON(http.StatusBadRequest, model.BadRequest("无效请求体"))
+	}
+
+	req.Name = strings.TrimSpace(req.Name)
+	if req.Name == "" {
+		return c.JSON(http.StatusBadRequest, model.BadRequest("名称不能为空"))
+	}
+
+	var result *filesystem.FileOperationResult
+	var err error
+
+	fullPath := filepath.Join(parentPath, req.Name)
+
+	switch req.Type {
+	case "dir":
+		result, err = h.fsSvc.CreateDir(fullPath)
+	default:
+		result, err = h.fsSvc.CreateFile(fullPath)
+	}
+
+	if err != nil {
+		return c.JSON(http.StatusInternalServerError, model.InternalError(err.Error()))
+	}
+	return c.JSON(http.StatusCreated, model.OK(result))
+}
+
+// Delete 删除文件或目录
+func (h *Handler) Delete(c echo.Context) error {
+	path := getPath(c)
+	result, err := h.fsSvc.DeletePath(path)
+	if err != nil {
+		return c.JSON(http.StatusInternalServerError, model.InternalError(err.Error()))
+	}
+	return c.JSON(http.StatusOK, model.OK(result))
+}
+
+// Rename 重命名文件或目录
+func (h *Handler) Rename(c echo.Context) error {
+	oldPath := getPath(c)
+	var req renameReq
+	if err := c.Bind(&req); err != nil {
+		return c.JSON(http.StatusBadRequest, model.BadRequest("无效请求体"))
+	}
+	req.NewPath = strings.TrimSpace(req.NewPath)
+	if req.NewPath == "" {
+		return c.JSON(http.StatusBadRequest, model.BadRequest("新路径不能为空"))
+	}
+	cleanNew := filepath.Clean(req.NewPath)
+	if strings.Contains(cleanNew, "..") {
+		return c.JSON(http.StatusBadRequest, model.BadRequest("新路径不允许包含 .."))
+	}
+	result, err := h.fsSvc.RenamePath(oldPath, cleanNew)
+	if err != nil {
+		return c.JSON(http.StatusInternalServerError, model.InternalError(err.Error()))
+	}
+	return c.JSON(http.StatusOK, model.OK(result))
+}
+
+// Upload 上传 Base64 编码的二进制文件
+func (h *Handler) Upload(c echo.Context) error {
+	path := getPath(c)
+	var req uploadReq
+	if err := c.Bind(&req); err != nil {
+		return c.JSON(http.StatusBadRequest, model.BadRequest("无效请求体"))
+	}
+	if req.Content == "" {
+		return c.JSON(http.StatusBadRequest, model.BadRequest("内容不能为空"))
+	}
+	if err := h.fsSvc.SaveBase64File(path, req.Content); err != nil {
+		return c.JSON(http.StatusInternalServerError, model.InternalError(err.Error()))
+	}
+	return c.JSON(http.StatusOK, model.NoContent())
+}
+
+// DetectType 通过文件内容检测类型
+func (h *Handler) DetectType(c echo.Context) error {
+	path := getPath(c)
+	info, err := h.fsSvc.DetectFileTypeByContent(path)
+	if err != nil {
+		return c.JSON(http.StatusOK, model.InternalError(err.Error()))
+	}
+	return c.JSON(http.StatusOK, model.OK(info))
+}