feat(M8): workspace isolation + SSH bottom file panel + context menu + monitor polish

- dual dockview workspaces (terminal/ssh), rail mode entries, sidebar filtered by mode
- SshBottomPanel: file browser below terminal, draggable divider; sftp.css finally imported (was orphaned since M4)
- file context menu: refresh/open/download/upload/rename/mkdir/copy-path/permissions/delete
- monitor restyle: memory amber bar, disk rows, net rx/tx inline (toFixed 4)
- completion fixes: Enter accepts; char-loss fixed by full-line rewrite (Ctrl+U) + echo-suppress ref
- chmod no-op fix: bitsToOctal concatenated decimal (329) instead of octal (511); chown only on change
- popups (layout menu/broadcast popover/file context menu) mount to body - dockview render overlay isolation clipped them under the sidebar
- rail slimmed: split + template actions folded into layout menu; log toolbar hover-only

docs/ROADMAP.md

@@ -14,6 +14,7 @@
 | M5 | 命令历史/命令库/补全 + 会话日志 | ✅ 已完成（v0.5） |
 | M6 | 广播输入 + ZMODEM + 快捷输入面板 + 快捷键系统 | ✅ 已完成（v0.6） |
 | M7 | 打包分发（MSI + NSIS + 自动更新） | ✅ 已完成（v0.7，Release 已发布） |
+| M8 | 工作区分离（Terminal/SSH 双工作区）+ SSH 底部文件面板 + 右键菜单 + 监控美化 + 补全修复 | ✅ 已完成（v0.8） |
 
 ## M2 — SSH 远程会话 ✅