feat: add IsLark field to FeishuConfig to switch between Feishu and Lark domains

[liuliqiang]

Add IsLark field to FeishuConfig to switch between Feishu and Lark domains. Also fix domain inconsistency where
WS client defaulted to LarkBaseUrl while HTTP client used FeishuBaseUrl.

📝 Description

Lark 是飞书的国际化版本，API 完全一致，唯一区别是域名：

• 飞书: https://open.feishu.cn (lark.FeishuBaseUrl)
• Lark: https://open.larksuite.com (lark.LarkBaseUrl)

本 PR 在 FeishuConfig 中新增 is_lark 字段（环境变量 PICOCLAW_CHANNELS_FEISHU_IS_LARK），设为 true
时自动将 HTTP client 和 WS client 的域名切换为 Lark 国际版。

同时修复了原有代码中 WS client 默认使用 LarkBaseUrl 而 HTTP client 使用 FeishuBaseUrl
的域名不一致问题，统一默认为 FeishuBaseUrl。

🗣️ Type of Change

• 🐞 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 📖 Documentation update
• ⚡ Code refactoring (no functional changes, no api changes)

🤖 AI Code Generation

• 🤖 Fully AI-generated (100% AI, 0% Human)
• 🛠️ Mostly AI-generated (AI draft, Human verified/modified)
• 👨‍💻 Mostly Human-written (Human lead, AI assisted or none)

🔗 Related Issue

N/A

📚 Technical Context (Skip for Docs)

• Reference URL: https://open.larksuite.com/document/server-v3/getting-started/api-access-process
• Reasoning: 飞书 SDK (github.com/larksuite/oapi-sdk-go) 已内置 lark.LarkBaseUrl 和 lark.FeishuBaseUrl
  常量以及 lark.WithOpenBaseUrl / larkws.WithDomain 选项，只需根据配置选择即可，无需额外依赖。

🧪 Test Environment

• Hardware: Mac (Apple Silicon)
• OS: macOS
• Model/Provider: N/A
• Channels: Feishu / Lark

📸 Evidence (Optional)

Click to view Logs/Screenshots

N/A（环境 Go 版本不匹配，未能本地运行完整构建，代码变更已通过人工审查确认正确性）

☑️ Checklist

• My code/docs follow the style of this project.
• I have performed a self-review of my own changes.
• I have updated the documentation accordingly.

[CLAassistant]

All committers have signed the CLA.

[yinwm]

LGTM! The core functionality is correctly implemented:

• API client correctly switches base URL using lark.WithOpenBaseUrl()
• WebSocket client correctly sets domain via larkws.WithDomain()
• Frontend form, i18n, and docs are complete

Two minor informational findings (non-blocking):

1. Log message shows "Feishu" regardless of IsLark config - cosmetic only
2. .env.example missing IS_LARK example - not affecting functionality

These can be addressed in a follow-up if desired.

[yinwm]

thanks for the pr

[Orgmar]

@liuliqiang 飞书和Lark域名切换这个功能很实用，通过一个 is_lark 字段就搞定了，同时还修复了 WS client 和 HTTP client 域名不一致的问题，考虑得很周全。

我们正在组建 PicoClaw Dev Group，方便贡献者们在 Discord 上交流协作。如果感兴趣的话，发封邮件到 support@sipeed.com，主题写 [Join PicoClaw Dev Group] liuliqiang，我们会把 Discord 邀请链接发给你！