feat: add HSL shift, contrast, and temporal blur CSPT filters

Three new processing template filters for both picture and color strip sources:
- HSL Shift: hue rotation (0-359°) + lightness multiplier via vectorized RGB↔HSL
- Contrast: LUT-based contrast adjustment around mid-gray (0.0-3.0)
- Temporal Blur: exponential moving average across frames for motion smoothing

server/src/wled_controller/static/js/core/filter-list.ts

@@ -26,6 +26,9 @@ const _FILTER_ICONS = {
     noise_gate:           P.volume2,
     palette_quantization: P.sparkles,
     css_filter_template:  P.fileText,
+    hsl_shift:            P.rainbow,
+    contrast:             P.slidersHorizontal,
+    temporal_blur:        P.timer,
 };
 
 export { _FILTER_ICONS };