Add target FPS slider to Capture Settings and remove unused HACS workflow

- Add Target FPS slider (range 10-90) to Capture Settings dialog
- Fix settings PUT to merge with current values instead of resetting defaults
- Update FPS validation range to 10-90 in schema and config
- Remove irrelevant .github/workflows/validate.yml (HACS leftover)

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

server/src/wled_controller/static/locales/en.json

@@ -152,6 +152,8 @@
   "settings.url.hint": "IP address or hostname of your WLED device",
   "settings.display_index": "Display:",
   "settings.display_index.hint": "Which screen to capture for this device",
+  "settings.fps": "Target FPS:",
+  "settings.fps.hint": "Target frames per second (10-90)",
   "settings.capture_template": "Capture Template:",
   "settings.capture_template.hint": "Screen capture engine and configuration for this device",
   "settings.button.cancel": "Cancel",