Add visual IconSelect selectors for effect, palette, gradient, waveform dropdowns

Replace plain <select> dropdowns with rich visual selectors:
- Effect type: icon grid with descriptions
- Effect/audio palette: gradient strip previews from color data
- Gradient preset: gradient strip previews (13 presets)
- Audio visualization: icon grid with descriptions
- Notification effect: icon grid with descriptions
- Waveform (value source): inline SVG shape previews

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/sw.js

@@ -7,7 +7,7 @@
  *   - Navigation: network-first with offline fallback
  */
 
-const CACHE_NAME = 'ledgrab-v18';
+const CACHE_NAME = 'ledgrab-v19';
 
 // Only pre-cache static assets (no auth required).
 // Do NOT pre-cache '/' — it requires API key auth and would cache an error page.