[BernardXiong]

Summary

• Default to the local SDK env-plugins JSON catalog when no explicit HTTP market is configured; preserve environment-variable and saved HTTP-market precedence.
• Resolve the highest compatible non-yanked artifact and download GitHub Release epacks using restricted HTTPS redirects, SHA-256 and size checks.
• Reuse existing package validation, unsigned-install consent, and transactional install/upgrade workflows; expose the SDK source in CLI and WebUI.
• Document the JSON catalog and publishing workflow in English and Chinese.
• Add CI for the full Python suite on Linux 3.10/3.12, SDK/HTTP market regression on Windows, and WebUI type checks, unit tests, deterministic assets and Chromium workflows.

Verification

• Local full Python suite, with isolated ENV_ROOT and no excluded tests: 350 passed, 2 skipped, 136 subtests passed.
• Frontend type check and production build passed; 30 frontend unit tests passed.
• Verified the committed Vue source reproduces the committed production JavaScript.
• Clean committed checkout: full Python regression passed after building the bundled epack; 17 Chromium SDK catalog and WebUI workflow tests passed.
• Real unauthenticated SDK Release download and isolated Kconfig 0.1.34 installation/backend/configuration smoke tests passed in the related SDK publication task.
• SDK catalog and first plugin release are published through Publish Kconfig as the first Env SDK plugin sdk#11.

Scope and Review

• Commits separate implementation, tests, CI, and documentation.
• Existing unrelated iframe popup-permission changes remain uncommitted locally and are not part of this PR.
• Do not merge automatically. Wait for all CI jobs and human review before merging.

[BernardXiong]

验证完成，当前提交 bc3e8c0 的 push / pull_request 两轮 CI 共 8 项检查全部通过：

• Linux Python 3.10 / 3.12：完整 Python 回归通过。
• Windows：SDK 索引、HTTP 市场、CLI 与 epack 回归通过。
• WebUI：类型检查、30 项单元测试、生产构建与静态产物一致性检查，以及 17 项 Chromium 端到端测试通过。
• 已修复干净检出中缺少内置 epack 构建产物的 CI 准备问题，未跳过失败测试。

CI 记录：

• Push: https://github.com/RT-Thread/env/actions/runs/42068324897
• Pull request: https://github.com/RT-Thread/env/actions/runs/42068341229

PR 保持打开，未启用自动合并，等待人工审核后合并。