feat: add initial AGENTS.md

AGENTS.md

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+# AGENTS.md - KIAUH Development Guide
+
+## Project Overview
+
+KIAUH (Klipper Installation And Update Helper) is a Python-based installation script for Klipper 3D printer firmware and related components written in Python 3.8+.
+
+## Running KIAUH
+
+```bash
+./kiauh.sh
+```
+
+**Important:** Must NOT run as root. The script will exit if EUID is 0.
+
+## Development Commands
+
+```bash
+# Install dev dependencies
+pip install -r requirements-dev.txt
+
+# Lint (ruff)
+ruff check .
+
+# Format
+ruff format .
+
+# Typecheck
+mypy kiauh
+
+# Run tests
+pytest
+
+# Run specific test file
+pytest kiauh/core/simple_config_parser/tests/public_api/test_options_api.py
+```
+
+## Testing
+
+- New tests should be placed near their corresponding components/modules (e.g., `kiauh/components/klipper/*/test_*.py`)
+- Always use a `tests/` subdirectory
+- Existing pytest setup in `kiauh/core/simple_config_parser/tests/` serves as reference
+
+## Project Structure
+
+- `kiauh.sh` - Bash entry point, sets PYTHONPATH and calls main.py
+- `kiauh/main.py` - Python entry point
+- `kiauh/core/` - Core functionality (menus, services, settings, types)
+- `kiauh/components/` - Klipper components (klipper, moonraker, webui_client, etc.)
+- `kiauh/extensions/` - Extension system for optional addons (obico, octoprint, spoolman, etc.)
+- `kiauh/core/simple_config_parser/` - Custom INI-style config parser for Klipper configs
+- `kiauh/core/simple_config_parser/src/simple_config_parser/` - Submodule (git subtree)
+
+## Key Quirks
+
+1. **Python version:** Requires Python 3.8+ (checked in kiauh.sh)
+2. **Config files:** KIAUH uses `kiauh.cfg` in project root (not .ini format - it's parsed by simple_config_parser)
+3. **Submodule:** `kiauh/core/simple_config_parser/` is a git subtree, not a submodule
+4. **Branch check:** KIAUH only checks for updates on master branch (not develop)
+5. **Target:** Designed to run on Raspberry Pi OS / Debian-based distros
+
+## Code Style
+
+- 4-space indentation
+- 88 character line length
+- Double quotes
+- LF line endings
+- Type hints required (mypy checks)
+- Ruff with I (isort) enabled