docs: 修复 openviking serve 命令引用并更新贡献文档

[qin-ctx]

Summary

• 将示例和脚本中失效的裸命令 openviking serve 统一替换为 openviking-server（openviking 入口已改为 Rust CLI 包装器）
• CONTRIBUTING 文档新增 Rust CLI 编译安装说明（cargo install --path crates/ov_cli）
• 修正 CONTRIBUTING 中测试示例：移除多余的 @pytest.mark.asyncio 装饰器（项目使用 asyncio_mode = "auto"）、更正测试文件路径和 fixture 用法
• 更新 CONTRIBUTING 项目结构，补充 server/、crates/ov_cli/、src/、测试子目录等缺失条目

Type of Change

• Documentation (docs)

Testing

• 文档变更，无需运行测试
• 手动确认所有 openviking serve 裸命令引用已替换
• python -m openviking serve 引用保持不变（仍可用）

Checklist

• Code follows project style guidelines
• Documentation updated
• 中英文 CONTRIBUTING 同步更新

🤖 Generated with Claude Code

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