feat(okx/hyperliquid): add Testnet/Simulated trading support

[guodage]

📝 Description | 描述

English: Add Testnet/Simulated trading support for OKX and Hyperliquid exchanges to enable safe strategy testing without real funds.

中文： 为 OKX 和 Hyperliquid 交易所添加测试网/模拟盘支持，允许在无需真实资金的情况下安全测试策略。

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🎯 Type of Change | 变更类型

• ✨ New feature | 新功能

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🔗 Related Issues | 相关 Issue

• Related to testnet environment setup

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📋 Changes Made | 具体变更

English:

• Added Testnet configuration property to AutoTraderConfig
• Updated OKX trader to support simulated trading header (x-simulated-trading: 1)
• Updated Hyperliquid trader to support testnet endpoint
• Added Testnet/Simulated trading toggle in UI for OKX and Hyperliquid
• Added i18n translations for testnet-related labels
• Updated API handlers to pass Testnet configuration when creating traders
• Refactored duplicate testnet fields into unified Testnet property

中文：

• 为 AutoTraderConfig 添加 Testnet 配置属性
• 更新 OKX trader 支持模拟盘头部 (x-simulated-trading: 1)
• 更新 Hyperliquid trader 支持测试网端点
• 在 UI 中为 OKX 和 Hyperliquid 添加测试网/模拟盘开关
• 添加测试网相关的 i18n 翻译
• 更新 API 处理程序在创建交易者时传递 Testnet 配置
• 重构重复的 testnet 字段为统一的 Testnet 属性

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🧪 Testing | 测试

• Tested locally | 本地测试通过
• Tests pass | 测试通过
• Verified no existing functionality broke | 确认没有破坏现有功能

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✅ Checklist | 检查清单

Code Quality | 代码质量

• Code follows project style | 代码遵循项目风格
• Self-review completed | 已完成代码自查
• Comments added for complex logic | 已添加必要注释

Documentation | 文档

• Updated relevant documentation | 已更新相关文档 (okx-api.md)

Git

• Commits follow conventional format | 提交遵循 Conventional Commits 格式
• Rebased on latest dev branch | 已 rebase 到最新 dev 分支
• No merge conflicts | 无合并冲突

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📚 Additional Notes | 补充说明

English:

• OKX uses the x-simulated-trading: 1 header for demo/paper trading accounts
• Hyperliquid connects to the official testnet endpoint when Testnet is enabled
• The UI shows different labels and descriptions based on the exchange type (OKX: "Use Simulated Trading", Hyperliquid: "Use Testnet")

中文：

• OKX 使用 x-simulated-trading: 1 头部来支持模拟/演示交易账号
• Hyperliquid 在启用 Testnet 时连接到官方测试网端点
• UI 根据交易所类型显示不同的标签和描述（OKX: "使用模拟盘", Hyperliquid: "使用测试网"）

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