Add unit tests for OpenAI plugin and establish coding standards

- Introduced comprehensive unit tests for the OpenAI plugin, covering SSE parsing, sentinel matching, delta extraction, request building, and more.
- Created a new markdown file detailing coding and naming conventions for the dstalk project, including guidelines for comments, naming rules, code organization, and memory management practices.

docs/reference/commands.md

@@ -13,7 +13,7 @@ dstalk 所有内置命令。在对话中直接输入 `/help` 或 `/h` 也可查
 | `/clear` | — | 清空当前会话上下文 | `/clear` |
 | `/context` | — | 显示当前 Token 数和消息条数 | `/context` |
 | `/status` | — | 显示当前运行状态 (脱敏: 不打印完整 API Key) | `/status` |
-| `/model <name>` | — | 切换 AI 模型 | `/model deepseek-v4-pro` |
+| `/model <name>` | — | 切换 AI 模型 | `/model gpt-4o` |
 | `/file list [path]` | — | 列出目录内容, 不填 path 列出当前目录 | `/file list src/` |
 | `/file show <path>` | — | 查看文件内容 | `/file show main.cpp` |
 | `/file read <path>` | — | 读取文件内容 (同 `/file show`) | `/file read config.toml` |