dsh-browser-bsk: BSK backend seam that provides ctx.browser

`dsh-browser-bsk` is a plugin designed to resolve `browser` service conflicts in the DeepSeek Harness plugin ecosystem. Instead of relying on a standalone Electron browser, it encapsulates the local `browser-skill` CLI as an injectable DSH `ctx.browser` service, coexisting with `browser-skill` while reusing its sessions. The plugin implements basic browser operations (such as opening, filling forms, clicking, and detecting CAPTCHAs) and supports only CSS selectors for element location. When installing, note that it is mutually exclusive with `dsh-builtin-browser`, and the path and timeout parameters can be adjusted via the configuration file.