refactor(client): 拆分 HTTP 客户端，分离嵌入模式与 HTTP 模式

[qin-ctx]

Description

拆分 HTTP 客户端为独立的 AsyncHTTPClient / SyncHTTPClient，与嵌入模式 (AsyncOpenViking / SyncOpenViking) 彻底分离，简化架构并消除模式混用。

Related Issue

N/A

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• 将 HTTPClient 重命名为 AsyncHTTPClient，新增 SyncHTTPClient 同步封装
• AsyncOpenViking / SyncOpenViking 仅保留嵌入模式，移除 url、api_key、user 参数
• AsyncHTTPClient 支持从 ovcli.conf 自动加载 url / api_key（未显式传入时）
• 移除所有客户端构造函数中的 user 参数，统一使用默认用户
• 简化 CLIContext，直接使用 SyncHTTPClient 替代 SyncOpenViking
• 简化 VikingFS._uri_to_path 实现
• search() 方法新增 session 参数，支持直接传入 Session 对象
• 更新中英文文档、示例代码和全部测试用例适配新 API

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

N/A

Additional Notes

这是一个 Breaking Change：

• AsyncOpenViking(url=...) 不再支持，HTTP 模式请改用 AsyncHTTPClient 或 SyncHTTPClient
• 客户端构造函数不再接受 user 参数

[CLAassistant]

All committers have signed the CLA.