Type of Change

• Bug fix (non breaking change, fixing an issue)
• New feature
• Breaking change (fix or feature that causes existing functionality to not work as expected)
• Documentation / Wiki update

Description

This introduces the optical Element Foil. Some preliminary dokumentation is included. But it will be adapted soon.
Fixed #issue

Optional notes for reviewer:
rayx-ui crashes when clicking the "surface" dropdown in Foil ( but also in gratings.

✅ Pre-Merge Checklist

Please complete each item before requesting a review.

• Code follows the project's coding standards
• Unit tests for new functionality are added and pass
• All existing tests pass
• Resolved TODO Comments (prefer new issues instead)
• Documentation, if applicable, including:
  • Doxygen comments for any new rayx-core API functions
  • Helpful inline comments where needed for clarity
  • Wiki pages, e.g. updated build instructions, new Element etc.
• Commits:
  • Use clear and readable commit messages (e.g. Conventional commits)
  • Squash and rebase onto master if individual commits don’t add value
  • Ensure linear commit history (required by master)