Add reusable icon-grid type selector for CSS source editor

Replaces the plain <select> dropdown with a visual grid popup showing
icon, label, and description for each source type. The IconSelect
component is generic and reusable for other type selectors.

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-v14';
+const CACHE_NAME = 'ledgrab-v15';
 
 // Only pre-cache static assets (no auth required).
 // Do NOT pre-cache '/' — it requires API key auth and would cache an error page.