feat(backgrounds): add matrix-rain background

src/locales/zh.json

@@ -1041,6 +1041,8 @@
       "snowfallDesc": "随风飘落的雪花",
       "starfield": "星空",
       "starfieldDesc": "向观察者飞来的星星",
+      "matrixRain": "黑客帝国雨",
+      "matrixRainDesc": "下落的字符列",
       "geminiEffect": "Gemini效果",
       "geminiEffectDesc": "类似Google Gemini的SVG效果",
       "speed": "速度",
@@ -1063,6 +1065,7 @@
       "multicolor": "多彩模式",
       "lineColor": "线条颜色",
       "wind": "风力",
+      "charset": "字符集",
       "bgColor": "背景颜色",
       "fillColor": "填充颜色",
       "color1": "颜色1",