Add Serbian translations and dark mode support

- Translated all UI text to Serbian
- Added dark mode toggle with system preference support
- Fixed text contrast on colored table rows
- Added dark mode styles throughout the app

src/components/ColorCell.tsx

@@ -8,18 +8,15 @@ interface ColorCellProps {
 export const ColorCell: React.FC<ColorCellProps> = ({ colorName }) => {
   const colorMapping = getFilamentColor(colorName);
   const style = getColorStyle(colorMapping);
-  const textColor = Array.isArray(colorMapping.hex) 
-    ? '#000000' 
-    : getContrastColor(colorMapping.hex);
 
   return (
     <div className="flex items-center gap-2">
       <div 
-        className="w-6 h-6 rounded border border-gray-300"
+        className="w-6 h-6 rounded border border-gray-300 dark:border-gray-600"
         style={style}
         title={Array.isArray(colorMapping.hex) ? colorMapping.hex.join(' - ') : colorMapping.hex}
       />
-      <span style={{ color: textColor }}>{colorName}</span>
+      <span>{colorName}</span>
     </div>
   );
 };