Convert novelkeys/nk87 to use RGB Matrix

[zvecr]

Description

Its been a while since we requested some movement on this, and this is one board I actually own. Follows the previous changes in #25450.

• Convert board away from custom RGB framework
• Tidy up
  • Migrate away from QMK_PROTON_C board files
  • Short form licence headers
  • Align readmes to template

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).