Add animation effects + double-buffered FPS optimization

- Add 5 new animation effects (strobe, sparkle, pulse, candle, rainbow
  fade) to both static and gradient color strip streams
- Fix FPS drops (30→25) by using 5ms re-poll on frame skip instead of
  full frame_time, preventing synchronization misses between animation
  thread and processing loop
- Double-buffer animation output arrays to eliminate per-frame numpy
  allocations and reduce GC pressure
- Use uint16 integer math for gradient brightness scaling instead of
  float32 intermediates
- Update animation type dropdowns and locale strings (en + ru)

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

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

@@ -596,11 +596,16 @@
   "color_strip.animation.enabled": "Enable Animation:",
   "color_strip.animation.enabled.hint": "Enables procedural animation. The LEDs will update at 30 fps driven by the selected effect.",
   "color_strip.animation.type": "Effect:",
-  "color_strip.animation.type.hint": "The animation effect to apply. Breathing works for both static and gradient sources; Gradient Shift and Wave work for gradient sources only.",
+  "color_strip.animation.type.hint": "The animation effect to apply. Breathing, Strobe, Sparkle, Pulse, Candle, and Rainbow Fade work for both static and gradient sources; Gradient Shift and Wave are gradient-only.",
   "color_strip.animation.type.breathing": "Breathing",
   "color_strip.animation.type.color_cycle": "Color Cycle",
   "color_strip.animation.type.gradient_shift": "Gradient Shift",
   "color_strip.animation.type.wave": "Wave",
+  "color_strip.animation.type.strobe": "Strobe",
+  "color_strip.animation.type.sparkle": "Sparkle",
+  "color_strip.animation.type.pulse": "Pulse",
+  "color_strip.animation.type.candle": "Candle",
+  "color_strip.animation.type.rainbow_fade": "Rainbow Fade",
   "color_strip.animation.speed": "Speed:",
   "color_strip.animation.speed.hint": "Animation speed multiplier. 1.0 ≈ one cycle per second for Breathing; higher values cycle faster.",
   "color_strip.color_cycle.colors": "Colors:",