codex-history-rail: Add a Codex-style turn timeline to DSH conversations

codex-history-rail adds a Codex-style turn timeline to the left side of the DeepSeek Harness Web interface chat area, supporting hover preview, click navigation, and cross-session favorites. Favorites are only stored locally in localStorage. The plugin is maintained by JAYCou, belongs to the client category, is a pure UI bundle with an empty Host side, only reads turnOutline and loaded turns, and does not import the DSH client package. Install using `dsh plugin add .` (execute in this package directory) and enable `@jaycou/codex-history-rail`. Version 1.0.2, License MIT, requires dsh >=0.2.1-rc.3 <0.3.0-0. Please note that the plugin runs with the current dsh process permissions; verify the source code and license before installation, and re-confirm version constraints after upgrading dsh. The plugin automatically hides on low resolutions, and favorites are not synced across devices. The source is the community directory SkillHub and has no official affiliation with DeepSeek or Mofang.