feat(M4): file permissions/ownership + monitor charts

- SftpEntry carries uid/gid/mode (drwxr-xr-x style) from readdir attrs
- chmod/chown via SSH exec (JD sftp subsystem silently ignores SETSTAT)
- FilePanel: permission + owner columns, chmod/chown dialog (rwx grid +
  octal input + uid/gid)
- MonitorPanel: canvas sparkline charts — CPU history (60 samples, 3min)
  and network rx/tx rates, dpr-aware, no deps
- tests: sftp-chmod real-server verification (chmod 700/755 round trip)

src/preload/index.ts

@@ -53,6 +53,10 @@ const api: AppApi = {
     ipcRenderer.invoke(Ipc.SFTP_RENAME, sessionId, from, to),
   deleteRemote: (sessionId: string, paths: string[]) =>
     ipcRenderer.invoke(Ipc.SFTP_DELETE, sessionId, paths),
+  chmodRemote: (sessionId: string, path: string, mode: string) =>
+    ipcRenderer.invoke(Ipc.SFTP_CHMOD, sessionId, path, mode),
+  chownRemote: (sessionId: string, path: string, uid: number, gid: number) =>
+    ipcRenderer.invoke(Ipc.SFTP_CHOWN, sessionId, path, uid, gid),
   uploadRemote: (sessionId: string, localPaths: string[], remoteDir: string) =>
     ipcRenderer.invoke(Ipc.SFTP_UPLOAD, sessionId, localPaths, remoteDir),
   downloadRemote: (sessionId: string, remotePaths: string[], localDir: string) =>