docs: Fully document icons-and-styling with validated CSS reference

- Add validation notice (verified against Unraid 7.2.3)
- Document Font Awesome 4.7.0 with size modifiers, animations, transformations
- Add complete CSS color palette reference (gray scale, brand colors, semantic ranges)
- Document status orb classes (.green-orb, .grey-orb, .blue-orb, .yellow-orb, .red-orb)
- Document text color classes (.green-text, .red-text, .orange-text, etc.)
- Add comprehensive utility classes (flexbox, text alignment, gap utilities)
- Update button styling documentation with validated classes
- Update custom CSS examples to use validated color variables
- Remove stub marker and placeholder images

Author: mstrhakr