dsh-task-manager: Add a floating task panel to DSH chat

`dsh-task-manager` is a DeepSeek Harness plugin maintained by caipanjin (npm package @caipj/dsh-task-manager, current version 1.1.5, MIT license). It provides a floating task panel in the bottom-right corner of the chat interface, supporting two sources: tasks suggested by the model via the `task_write` tool and tasks manually added by the user, with a source badge on each line. Selected dialogue text or list items can be used to create tasks directly (tasks are created item-by-item based on the DOM `<li>` structure). Status is indicated by a dot and text; when the model reports completion, it only proposes tasks, which are finalized by the "Confirm All / Ignore" banner, and clicking "Start" sends them to the dialogue only after a second confirmation. The panel's position is saved by the browser and supports both light and dark modes as well as Chinese and English bilingual interfaces. Installation can be performed via `dsh plugin --profile web add @caipj/dsh-task-manager` or by installing from the source code at github:caipanjin/dsh-task-manager, requiring a restart of the host afterward. The plugin runs with the permissions of the current dsh process; source code and license should be reviewed before installation.