feat(client): ovcli.conf 支持 timeout 配置 + 修复 Rust CLI agent_id

[qin-ctx]

Description

为 Python 和 Rust CLI 客户端添加通过 ovcli.conf 配置 HTTP 超时的支持，同时修复 Rust CLI 未正确读取 agent_id 的问题。

Related Issue

Closes #306

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Documentation update

Changes Made

• Python HTTP 客户端 (openviking_cli/client/http.py): 从 ovcli.conf 读取 timeout, 优先级: SDK 显式传参 > ovcli.conf > 默认值 60.0
• Python 同步客户端 (openviking_cli/client/sync_http.py): 透传 timeout 参数到 AsyncHTTPClient
• Rust CLI 配置 (crates/ov_cli/src/config.rs): 将未使用的 user 字段替换为 agent_id, 新增 timeout 字段 (serde 默认 60.0)
• Rust CLI 客户端 (crates/ov_cli/src/client.rs): 接收 agent_id 和 timeout_secs 参数, 发送 X-OpenViking-Agent 请求头, 与 Python 客户端对齐
• Rust CLI 入口 (crates/ov_cli/src/main.rs): 将配置中的 agent_id 和 timeout 传递给 HttpClient
• 文档: 将 timeout 文档从 configuration guide 移至 API overview (中英文)
• 示例: ovcli.conf.example 加入 timeout 字段, 更新代码示例

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 made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Additional Notes

Rust CLI 此前有一个从未使用的 user 字段, 且不支持 agent_id 和可配置超时。本 PR 将 Rust CLI 与 Python 客户端对齐:

1. 从 ovcli.conf 读取 agent_id 并作为 X-OpenViking-Agent 请求头发送
2. 从 ovcli.conf 读取 timeout 并应用到 reqwest HTTP 客户端

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