feat(backgrounds): add snowfall background

src/locales/en.json

@@ -1155,6 +1155,8 @@
       "rippleDesc": "Ripple wave effect",
       "fireflies": "Fireflies",
       "firefliesDesc": "Drifting glowing dots with pulsation",
+      "snowfall": "Snowfall",
+      "snowfallDesc": "Falling snow with wind drift",
       "geminiEffect": "Gemini Effect",
       "geminiEffectDesc": "SVG effect like Google Gemini",
       "speed": "Speed",
@@ -1176,6 +1178,7 @@
       "explosionColor": "Explosion Color",
       "multicolor": "Multicolor",
       "lineColor": "Line Color",
+      "wind": "Wind",
       "bgColor": "Background Color",
       "fillColor": "Fill Color",
       "color1": "Color 1",