dsh-split-view: DeepSeek Harness Multi-Session Split-Screen Plugin

The `dsh-split-view` plugin is designed to address the pain point of switching between multiple concurrent sessions. Inspired by terminal split-screen logic, it transforms the main DSH window into a multi-pane container. The plugin supports freely nested horizontal and vertical layouts, drag-to-resize panes, and core features such as double-click to enlarge, renaming via the title bar, copying session information, and interacting with other plugins through the Cordis service. Installation requires the DSH command-line tool and supports local development and debugging. The plugin includes default shortcuts and allows users to customize key combinations, selection highlight colors, and hide title bars. It also provides a robust error handling mechanism.