Enhance Env WebUI and plugin development workflows

[BernardXiong]

概述 / Summary

完善 Env 的 WebUI 项目体验和插件开发流程，统一网络配置，并改进命令行失败处理及远程浏览器启动。
Improve the Env WebUI project experience and plugin development workflows, unify network configuration, and improve CLI failure handling and remote browser launching.

主要变更 / Changes

• 项目首页 / Project Home
  支持后台 SCons 构建、清理、日志查看及 ELF 产物展示。
  Support background SCons builds, cleanup, build logs, and ELF artifact discovery.

• 项目文档 / Project Documents
  支持 Markdown、目录、代码高亮、图片、Mermaid 和 PlantUML，并限制工作区资源访问范围。
  Render Markdown, tables of contents, syntax highlighting, images, Mermaid, and PlantUML with workspace-bounded resource access.

• 网络设置 / Network Settings
  统一代理、GitHub/Gitee 下载选择、PyPI 源和超时配置，接入包管理、SDK、插件市场及 Python 引导。
  Share proxy, GitHub/Gitee download selection, PyPI index, and timeout policies across package management, SDK downloads, the plugin market, and Python bootstrapping.

• 命令行可靠性 / CLI Reliability
  传播失败结果和退出码，确保 SDK 操作恢复工作目录、参数及环境上下文。
  Propagate failures and exit codes, and restore the working directory, arguments, and environment context after SDK operations.

• 插件清单 / Plugin Manifests
  支持 SVG/PNG 图标及工作区启动条件，补充打包校验和安装诊断。
  Support SVG/PNG icons and workspace launch requirements, with package validation and installation diagnostics.

• 插件开发工具 / Plugin Development Kit
  新增 epack test、push/publish 工作流，官方插件升级至 1.1.0。
  Add epack test and push/publish workflows, and upgrade the official plugin to version 1.1.0.

• 浏览器启动 / Browser Launching
  支持 VS Code Server helper 和 Remote CLI，避免桥接失败时误启动远程系统浏览器。
  Open URLs through the VS Code Server helper or Remote CLI without launching a remote system browser when the bridge fails.

• 文档与静态资源 / Documentation and Static Assets
  同步中英文文档、前端依赖和静态构建产物。
  Update bilingual documentation, frontend dependencies, and generated static assets.

验证 / Validation

• Python 回归测试 / Python regression tests: 230 passed, 2 skipped.
• 前端单元测试 / Frontend unit tests: 26 passed.
• Playwright E2E: 16 passed, 1 skipped，覆盖桌面和移动端 / covering desktop and mobile.
• TypeScript 类型检查通过 / TypeScript type checking passed.
• 生产构建通过，重建产物与已提交静态资源逐文件一致。
  Production build passed; rebuilt assets matched the committed static resources byte-for-byte.

行为说明 / Behavior Notes

• 未指定插件时，WebUI 默认进入项目首页。
  WebUI opens the project home by default when no plugin is specified.
• 网络设置仅作用于 Env 请求和子进程，不修改全局 Git、pip 或 Shell 配置。
  Network settings apply only to Env requests and child processes, without modifying global Git, pip, or shell configuration.
• epack test 使用临时安装目录，不提供权限隔离沙箱。
  epack test uses a temporary installation directory and does not provide a security sandbox.
• PlantUML 在线渲染会向外部服务发送图表源码；敏感图表应使用本地 Mermaid。
  Online PlantUML rendering sends diagram source to an external service; use local Mermaid rendering for sensitive diagrams.