fix(studio): restore Feishu config during runtime updates

[evanlowe]

Summary

• restore Feishu App ID and App Secret when reopening a Runtime update
• persist complete Studio drafts while keeping MCP credentials ephemeral
• preserve, replace, or remove Feishu Runtime environment variables explicitly during updates
• regenerate projects when the Feishu channel selection changes
• preserve existing MCP configuration and configured credential markers

Validation

• frontend: 964 tests passed
• Python Studio and Feishu regression suites: 134 tests passed
• additional Runtime recovery suite: 224 tests passed
• production WebUI build and packaged asset verification passed
• pre-commit Ruff, formatting, and Gitleaks passed
• desktop 1600x900 and mobile 390x844 Studio update flows visually verified
• Volcengine and BytePlus preserve/replace/remove update matrix covered

[evanlowe]

端到端验收完成：

• 新建 Runtime studio-feishu-e2e-20260903-094528（r-yeu8vjlc74dkhuksvx89），首次部署与原地更新均成功
• 更新后再次进入编辑页，Agent 基础属性、模型/API Key 元数据、Tool、MCP、Memory、Tracing、子 Agent、公网与飞书 App ID/App Secret 均正确回显
• 专用飞书机器人 testagent WebSocket 连接正常；用户实测发送消息后已收到机器人回复
• 已 rebase 到最新 origin/main，提交为 5ebbcdc1
• 本地：前端 964 项、后端相关 126 项、WebUI 资源校验、pre-commit 全部通过
• GitHub CI 全部通过