docs: Add responsive WebGUI and dashboard tile documentation for Unraid 7.2+

Based on the official Responsive WebGUI Plugin Migration Guide by ljm42 (Unraid Administrator)

Source: https://forums.unraid.net/topic/192172-responsive-webgui-plugin-migration-guide/

- Complete rewrite of dashboard-tiles.md with new tile-header structure

- New responsive-design.md covering common bugs, fixes, and migration

- Updated UI index to highlight responsive design section

- Added ljm42 attribution to attributions.md

Author: mstrhakr

docs/attributions.md

@@ -20,6 +20,14 @@ This project complies with the [Third-Party App Naming & Trademark Use Policy](h
 
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+## Responsive WebGUI Migration Guide
+
+The responsive design and dashboard tiles documentation is based on the official [Responsive WebGUI Plugin Migration Guide](https://forums.unraid.net/topic/192172-responsive-webgui-plugin-migration-guide/) by **ljm42** (Unraid Administrator), published July 21, 2025.
+
+Used with permission — ljm42 granted permission for use in open-source plugin templates and documentation (see forum thread).
+
+---
+
 ## GitHub
 
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