Fix oversized icons in category navigation

[bblumenfelder]

Problem

Icons in the custom SQL query overview were displayed too large, particularly in non-core plugins where the CSS rules weren't being applied correctly.

Solution

• Replaced background-image based icons with Font Awesome icons
• Fixed icon sizing to a consistent 28px
• Added proper CSS styling for expand/collapse states using transform rotation
• Improved button layout with Bootstrap flex utilities

This fixes the issue where CSS rules for background images weren't properly applied in non-core plugin contexts.