Added comprehensive user documentation for visual dashboard customization:
- docs/user/icon-colors.md: New guide for using icon_color attribute
* Explains CSS variable approach for theme compatibility
* Shows when to use icon_color vs state interpretation
* Examples for Custom Button Card, Entities Card, Mushroom, Glance
* Custom color override options (theme-based and direct)
* All state values use lowercase (HA convention)
- docs/user/dynamic-icons.md: New guide for automatic icon changes
* Explains state-based icon behavior without cataloging specifics
* Dashboard examples with standard and custom cards
* Icon override instructions for fixed icons
* Binary sensor icon behavior details
* Integration with dynamic colors
- Updated cross-references in README.md, sensors.md, automation-examples.md
to link both new guides
Impact: Users can now create visually rich dashboards with color-coded and
icon-changing sensors without writing complex conditional logic. Documentation
focuses on principles and practical examples rather than exhaustive listings,
making it easy to understand and maintain.