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)

.gitignore

@@ -5,6 +5,8 @@ node_modules/
 out/
 dist/
 tests/.session-e2e.cjs
+tests/.sftp-svc.*
+tests/.hl-smoke.*
 
 # research artifacts (XTerminal reverse-engineering notes, not part of the app)
 research/