Add collapsible pipeline metrics and error indicator to target cards

FPS chart stays always visible; timing, frames, keepalive, errors, and
uptime are collapsed behind an animated toggle. Error warning icon
appears next to target name when errors_count > 0. Uses CSS grid
0fr→1fr transition for smooth expand/collapse animation.

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-v17';
+const CACHE_NAME = 'ledgrab-v18';
 
 // Only pre-cache static assets (no auth required).
 // Do NOT pre-cache '/' — it requires API key auth and would cache an error page.