Integrate AGENTS.md (#203)

From https://agents.md to integrate an open-source format
for guiding coding agents. The main concept is basically this:

* `README.md`: designed for humans.
* `AGENTS.md`: designed for AI coding agents.

Author: tomschr

AGENTS.md

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+# Docbuild Project
+
+This document outlines key information about the `docbuild` project to assist AI agents and developers.
+
+## Purpose of this Project (Docbuild)
+
+Docbuild builds documentation from DocBook 5/ASCIIDoc, manages XML configs, clones repos, runs `daps`, handles metadata and syncing deliverables.
+
+## Repository Facts
+
+* **Python Version:** >= 3.12
+* **Package Manager:** `uv` (Astral)
+* **Key Directories:**
+  * `src/`: Source code
+  * `tests/`: Test suite (pytest)
+  * `.github/workflows/`: CI/CD configurations
+* **CLI Entry Point:** `docbuild` (file `src/docbuild/__main__.py`)
+* **Documentation:*** https://opensuse.github.io/docbuild/
+
+## Setup
+
+1. Create a virtual environment with `uv venv`
+2. Install dependencies: `uv sync --frozen --group devel`
+
+## Testing with `uv`
+
+To run tests in this environment, use the following commands:
+
+* **Run complete test suite:**
+
+  ```bash
+  uv run --frozen pytest
+  ```
+
+* **Run single test file:**
+
+    ```bash
+    uv run --frozen pytest tests/path/to/test_file.py
+    ```

changelog.d/203.infra.rst

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+Add :file:`AGENTS.md` for guiding coding agents.