This pull request introduces important onboarding and security improvements to the repository. The main changes include adding repository-specific onboarding instructions for Copilot coding agents, and incorporating two new GitHub Actions workflows: one for advanced CodeQL code scanning and another for generating SLSA provenance files to enhance supply chain security.

Repository onboarding and documentation:

• Added .github/copilot-instructions.md with detailed guidelines to help Copilot coding agents efficiently understand, build, test, and validate changes in the repository, aiming to reduce build failures and improve agent productivity.

Security and workflow enhancements:

• Introduced .github/workflows/codeql.yml to enable advanced CodeQL code scanning for multiple languages, improving automated detection of security vulnerabilities and code quality issues on push, pull request, and scheduled events.
• Added .github/workflows/generator-generic-ossf-slsa3-publish.yml to automate the generation of SLSA Level 3 provenance files for project artifacts, supporting secure software supply chain practices and artifact verification.

Originally posted by @JaclynCodes in #1006 (comment)