[brunoborges]

Description:
Add repository-specific guidance for future Copilot sessions, including build/test/lint commands, architecture, key conventions, and behavior principles drawn from the action's documentation.

Related issue:
N/A

Check list:

• Ran npm run check locally (format, lint, build, test) and all checks pass.
• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

[Copilot]

🟢 Approval recommended

The documentation-only addition of repository-specific Copilot guidance has no active review issues.

No open issues 🎉

What changed in this PR

Adds repository-specific Copilot guidance to help future sessions follow the setup-java action’s architecture, development conventions, and documented behavior. This is a documentation-only change.

Changes:

• Documents build, test, lint, and formatting commands.
• Explains runtime entrypoints, installer architecture, and repository conventions.
• Records behavior requirements for version selection, caching, verification, and Maven configuration.

File	Description
.github/​copilot-instructions.md	Adds development guidance and action behavior principles for future Copilot sessions.

_{Review effort: Balanced}