Upgrade bundled axe-core to v4.13.0 and add AGENTS.md upgrade instructions

[Copilot]

Scheduled CI checks flagged an available update for the bundled axe-core JavaScript engine. This PR upgrades the bundled distribution to the latest release and documents the maintenance workflow for future automation agents.

Key Changes

• Axe Core Upgrade: Updated axe_playwright_python/axe.min.js to v4.13.0 using the internal installation script.
• Agent Documentation: Created AGENTS.md at the repository root with step-by-step instructions for upgrading the bundled axe-core asset and running validation checks.

Usage Example

# Upgrade axe-core to latest release
bash .github/scripts/install-axe.sh

# Target a specific release version
bash .github/scripts/install-axe.sh 4.13.0

• Fixes Upgrade axe #27

[pamelafox]

@copilot Also update changelog-
https://github.com/pamelafox/axe-playwright-python/pull/23/changes

and pyproject.toml
e8ddc07

[Copilot]

@copilot Also update changelog-
https://github.com/pamelafox/axe-playwright-python/pull/23/changes
...

Updated CHANGELOG.md and bumped version to 0.1.9 in pyproject.toml in commit a69b3f6.