feat(v1.2): 体验升级 — 快捷键系统 + 标签拖拽 + SFTP拖拽上传 + 组件拆分 + 响应式

任务1: 全局快捷键管理器 — useKeyboardShortcuts hook
  Ctrl+Tab/Shift+Tab标签切换, Ctrl+1~9跳转, F11全屏, Ctrl+Shift+N新建标签

任务2: 标签拖拽排序 — tabStore.moveTab + TabBar HTML5 DnD
  不可变更新, 拖拽视觉反馈(opacity+指示线), 活跃标签底部accent-blue指示线

任务3: SFTP拖拽上传 + useSFTP调试清理
  FileListPanel拖拽覆盖层(Upload图标+虚线边框), 5个调试函数→createLogger,
  disconnect()正确调用IPC, 删除mock data

任务4: SFTP右键菜单完善 — 重命名/复制路径/属性/权限
  FilePropertiesDialog+ChmodDialog, sftpStat/sftpChmod IPC全栈实现

任务5-6: 侧边栏分组折叠动画 + 宽度可拖拽调整
  Grid 0fr→1fr折叠动画, ChevronRight旋转, resize handle 180~400px, settings记忆

任务7: 响应式布局 + 视觉优化V1~V5
  useMediaQuery hook, <800px侧边栏overlay模式, SFTP垂直堆叠, WelcomeView响应式grid

任务8: Loading/Skeleton骨架屏
  Skeleton/SkeletonLine/SkeletonCircle/SkeletonBlock + FileListSkeleton/SessionTreeSkeleton/TabContentSkeleton

任务9: 空状态设计
  EmptyState通用组件, SessionTree/FileListPanel/WelcomeView/SFTPView空状态引导

任务10: TerminalView组件拆分重构 711行→285行
  useTerminalConnection(300行) + useTerminalSearch(123行)
  + TerminalOverlay(98行) + TerminalSearchBar(74行)

33 files changed, 2682 insertions(+), 872 deletions(-)

electron/preload.ts

@@ -25,6 +25,8 @@ const api = {
   sftpRename: (sftpId: string, oldPath: string, newPath: string) => ipcRenderer.invoke('sftp:rename', sftpId, oldPath, newPath),
   sftpDelete: (sftpId: string, path: string, isDirectory: boolean) => ipcRenderer.invoke('sftp:delete', sftpId, path, isDirectory),
   sftpMkdir: (sftpId: string, path: string) => ipcRenderer.invoke('sftp:mkdir', sftpId, path),
+  sftpStat: (sftpId: string, filePath: string) => ipcRenderer.invoke('sftp:stat', sftpId, filePath),
+  sftpChmod: (sftpId: string, filePath: string, mode: number) => ipcRenderer.invoke('sftp:chmod', sftpId, filePath, mode),
 
   // 端口转发
   sshForwardLocal: (connectionId: string, localPort: number, remoteHost: string, remotePort: number) =>