docs: 修正 assets/docs/ 类图、数据流、参数文档及贡献指南

- design.md: 新增 ProtocolHandler/OpenAIHandler/AnthropicHandler 等缺失类
- design.md: 新增 Template Method、Storage 设计模式
- dataflow.md: 修正 GQA/MLA 为独立条目，补充 JSON 存储后端
- params.md: 标注 label_smoothing CLI 默认与 strategy 默认差异
- introduction.md: 修正 max_tokens 默认值 1024→2048
- CONTRIBUTING.md: 重写（纯 Python 无 conda、补充 CI 步骤与常见问题）
- .github/PULL_REQUEST_TEMPLATE.md: 修正 lint 命令，去除多余注释要求
- .github/ISSUE_TEMPLATE/bug_report.md: 修正 label（enhancement→bug）

.github/PULL_REQUEST_TEMPLATE.md

@@ -16,9 +16,9 @@ Please delete options that are not relevant.
 Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce.
 
 ## Checklist:
-- [ ] My code follows the style guidelines of this project (run `ruff format .` and `ruff check --fix .`)
+- [ ] My code follows the style guidelines of this project (run `ruff format .` and `ruff check . --select I`)
 - [ ] I have performed a self-review of my own code
-- [ ] I have commented my code, particularly in hard-to-understand areas
+- [ ] Code is self-documenting (no unnecessary comments)
 - [ ] I have made corresponding changes to the documentation
 - [ ] My changes generate no new warnings
 - [ ] I have added tests that prove my fix is effective or that my feature works