Connect DeepSeek Harness to AI SDK with ai-sdk-provider-dsh

The `ai-sdk-provider-dsh` is maintained by krislavten, which wraps the DeepSeek Harness runtime into AI SDK's LanguageModelV3, compatible with both v6 and v7. The application side still uses `generateText` / `streamText`, and actually spawns a `dsh` subprocess pinned to version 0.1.0-rc.6. Tools are executed within the harness, and a fixed `sessionId` can be used to resume conversations. The main installation method is via npm; the directory page command is `dsh plugin add github:krislavten/ai-sdk-provider-dsh`. Node.js ≥22.19 is required, and `dsh` is still in developer preview.