Add OpenRGB per-zone LED control with separate/combined modes and zone preview

- Zone picker UI in device add/settings modals with per-zone checkbox selection
- Combined mode: pixels distributed sequentially across zones
- Separate mode: full effect resampled independently to each zone via linear interpolation
- Per-zone LED preview in target cards: one canvas strip per zone with hover overlay labels
- Zone badges on device cards enriched with actual LED counts from OpenRGB API
- Fix stale led_count by using device_led_count discovered at connect time

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-v2';
+const CACHE_NAME = 'ledgrab-v6';
 
 // Only pre-cache static assets (no auth required).
 // Do NOT pre-cache '/' — it requires API key auth and would cache an error page.