Add root-level AI agent rules for repository-scoped behavior

[Copilot]

This adds a repository-level AGENTS.md for Codex-like agents working in rt-thread. It defines, in a very concise bilingual format, what agents may do, what they must not do, and the minimal placement and precedence rules for repository-scoped behavior.

• What this adds

  • Introduces /AGENTS.md at the repository root as the single entry point for AI-agent-specific rules.
  • Encodes the core operating principle for agents: minimal, task-focused, verifiable changes.

• Allowed / prohibited behavior

  • Lists permitted actions such as reading task-relevant files, making minimal targeted edits, and updating directly related docs/tests when needed.
  • Explicitly forbids unrelated refactors, bulk formatting, generated artifacts, secret insertion, dependency churn, third-party/imported code changes unless explicitly required, test weakening/removal, and history-rewrite behaviors.
  • Explicitly forbids casually creating new Markdown documents without clear instructions.
  • Explicitly forbids hand-editing BSP rtconfig.h, requiring it to be generated from .config via scons --menuconfig or scons --pyconfig-silent.

• Repository structure rules

  • Keeps a concise placement rule referencing the existing top-level layout: bsp/, components/, documentation/, examples/, include/, libcpu/, src/, and tools/.
  • Clarifies that repository-entry documents such as AGENTS.md, README.md, and LICENSE belong in the root, while general documentation should live under documentation/.
  • Adds explicit placement rules: BSP code in bsp/, kernel code in src/, tests/examples in examples/, component code in components/, abstracted driver code in components/drivers/, and shared chip/architecture porting code in libcpu/.
  • States that code must be placed in the proper existing directories and that new subdirectories under major directories must not be created arbitrarily.

• Rule precedence

  • States that more specific repository guidance takes precedence when rules overlap, with explicit references to:
    • .github/CONTRIBUTING.md
    • documentation/7.contribution/coding_style_cn.md
    • documentation/7.contribution/coding_style_en.md

• Presentation

  • Uses a very concise Chinese-English bilingual format throughout so the document is immediately scannable for both human contributors and tooling.

Example excerpt:

## Strictly forbidden / 严格禁止

- Creating Markdown documents without explicit instructions. / 没有明确指令时，禁止随意新建 Markdown 文档。
- Placing code in the wrong directory or creating new subdirectories under major directories without a clear requirement. / 禁止乱放代码，禁止在主要目录下无明确要求时新建子目录。
- Editing a BSP `rtconfig.h` by hand; generate it from `.config` with `scons --menuconfig` or `scons --pyconfig-silent`. / 禁止手工修改 BSP 的 `rtconfig.h`；应通过 `scons --menuconfig` 或 `scons --pyconfig-silent` 基于 `.config` 生成。

## Placement / 放置规则

- BSP code only in `bsp/`; kernel code in `src/`; tests/examples in `examples/`; component code in `components/`; abstracted driver code in `components/drivers/`; chip or architecture shared porting code in `libcpu/`. / 板级支持包代码只放在 `bsp/`；内核代码放在 `src/`；测试/例程代码放在 `examples/`；组件代码放在 `components/`；抽象层驱动相关代码放在 `components/drivers/`；芯片或架构公共移植代码放在 `libcpu/`。

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[BernardXiong]

@copilot
需要更简洁些：非常简洁的给出可以做什么（或者说是什么），严格禁止做什么，同时也是中英双语的方式。

[Copilot]

@copilot
需要更简洁些：非常简洁的给出可以做什么（或者说是什么），严格禁止做什么，同时也是中英双语的方式。

已按意见精简并改成中英双语的简洁规则页，提交为 4af2e21c。

[BernardXiong]

@copilot
加入以下内容：

• 板级支持包只放在 bsp 目录下；
• 内核的代码放在 src 目录下；
• 测试/例程代码放在 examples 目录下；
• 组件相关的代码放在 components 目录下
  • 和抽象层驱动相关代码放在 components/drivers 目录下；
• 芯片、芯片架构的公共移植代码放在 libcpu 目录下；

代码位置都理顺，放置好，严禁乱放，在主要的目录下新生成子目录。严禁在使用AI Agent过程中，随意生成 markdown 文档，而应该有明确指令才生成 markdown 文档。

另外，对于每个bsp来说，rtconfig.h 不应该被手工修改，而是由 scons --menuconfig 或 scons --pyconfig-silent 来根据 .config 配置生成。

[Copilot]

@copilot
加入以下内容：

• 板级支持包只放在 bsp 目录下；
  ...

已补充并提交，提交为 640c4349。