dsh-stickerbook: Add a local sticker library to DeepSeek Harness

`dsh-stickerbook` is a local sticker plugin for DeepSeek Harness maintained by Asgoresmilelong. It comes with 157 Chinese stickers and supports searching by emotion tags or keywords. The button to the left of the input box provides a searchable gallery where users can send a sticker with a single click. On the assistant side, it only stores pure text tokens in the format `[sticker: description]`, which are rendered into images by the client, bypassing the limitation where the host Markdown renderer does not recognize local or HTTP images. When the host has the companionQq service, `action=send` allows sending original images natively. The plugin provides four tools: `send_sticker`, `sticker_list`, `sticker_learn`, and `sticker_update`. Adding stickers requires zero configuration (choose one of: dropping files, agent indexing, or manually editing `stickers.json`). The host side relies solely on built-in Node modules, without a database or native extensions. It is important to note that the sticker materials are all sourced from Bilibili @赤风RED, licensed under CC BY-NC 4.0, and the code is MIT licensed; commercial use of the materials requires separate authorization.