build(agents): provide GitHub Copilot agent files

[spliffone]

reference #1491

Describe in detail what your merge request does and why. Add relevant
screenshots and reference related issues via Closes #XY or Related to #XY.

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• I confirm that this MR follows the contribution guidelines.

[gemini-code-assist]

Code Review

This pull request introduces two GitHub Copilot agent definition files, docs-agent.md and test-agent.md. The definitions are a great start for leveraging AI in the development workflow. I've made a few suggestions to improve the clarity and correctness of the agent instructions. In docs-agent.md, I've suggested an alternative for a missing npm script. In test-agent.md, I've pointed out that the code style example is missing and that the 'Boundaries' section is malformed and incomplete, providing a suggestion to fix it, aligning with the preference for clear and comprehensive documentation.

[gemini-code-assist]

This "Code style example" section is empty. Providing a concrete code snippet that demonstrates the expected style for tests would make the agent's instructions much clearer and more effective.

[github-actions]

[github-actions]

Documentation.
Examples.
Playwright report.

Coverage Reports:

• element-ng
• element-translate-ng