Document root env configuration

[yiguodev]

Summary

• Document the root-level env object in Chinese, English, and Russian.
• List supported runtime env keys and preload-only env keys.
• Add env to the root configuration overview pages.

Validation

• pnpm docs:build
• git diff --check

[Copilot]

Pull request overview

This PR expands the configuration documentation to cover the root-level env object across Chinese, English, and Russian docs, and links it from the root configuration overview pages.

Changes:

• Added "env": {} to the root configuration JSON examples in CN/EN/RU overview pages.
• Added env to the “Basic/Basics configuration modules” lists in CN/EN/RU index pages with a short description.
• Expanded the CN/EN/RU env feature pages to document the root env object (supported keys, string value requirement, and priority/restrictions).

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
docs/ru/config/index.md	Adds env to the RU root config example and module list.
docs/ru/config/features/env.md	Documents RU root-level env object, supported keys, and precedence/restrictions.
docs/en/config/index.md	Adds env to the EN root config example and module list.
docs/en/config/features/env.md	Documents EN root-level env object, supported keys, and precedence/restrictions.
docs/config/index.md	Adds env to the ZH root config example and module list.
docs/config/features/env.md	Documents ZH root-level env object, supported keys, and precedence/restrictions.

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[yiguodev]

@RPRX 改好了。

[RPRX]

文档只保留大写的那种吧（虽然代码仍兼容小写），对环境变量的介绍分为三段，3+2+N，对于 N 像之前一样简单列一下即可

@Fangliding @Meo597 然后你俩看下没问题就合了吧，不用等发版

[yiguodev]

已调整。

[RPRX]

看文档发现两个问题，一是应该叫“环境变量”而不是“环境配置”，不知道的还以为要配置环境，二是侧边栏“特性详解”跑下面了

[Meo597]

我来搞一下吧

[Meo597]

好了 93302d5

[RPRX]

@Meo597 #874 (comment)

[Fangliding]

本来正文已经写好了怎么修格式还把正文改了

[Meo597]

以前莫名引入了一个 根 env 的概念云里雾里的，我看到下意识认为是不是还能继续套娃
还大篇幅写了 env 生效时机，但用户不可能去硬翻代码
以及进程和实例的概念，xray 应该没法一个进程跑多个实例吧现在

也没讲怎么用 shell 设环境变量，现在既然提到了 conf 必须通过它就应该讲一下

所以我直接重做了这一页

[RPRX]

这下听得我云里雾里的

总之至少文档别保留小写

[Meo597]

可能跟他那个 PR 最开始的实现方式有关系
一开始不是 os.SetEnv 因此一个进程内的多个实例是各自独立的
文档有了这个概念又没完全解释清楚

不提小写
3+2+n 顺序调了
加了几个 go 的 env

改好了