Add color correction postprocessing filter

New filter with color temperature (2000-10000K) and per-channel RGB
gain controls. Uses LUT-based processing for fast per-frame application.

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

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

@@ -293,6 +293,7 @@
   "filters.pixelate": "Pixelate",
   "filters.auto_crop": "Auto Crop",
   "filters.flip": "Flip",
+  "filters.color_correction": "Color Correction",
   "postprocessing.description_label": "Description (optional):",
   "postprocessing.description_placeholder": "Describe this template...",
   "postprocessing.created": "Template created successfully",