Add dark mode option

src/components/theme-selector.tsx

@@ -0,0 +1,29 @@
+/**
+ * Theme Selector Component
+ *
+ * Provides UI for switching between light/dark/system theme modes.
+ * Uses shadcn/ui Select component.
+ *
+ * @author Andreas Weyer
+ * @license MIT
+ */
+
+import React from 'react';
+import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from './ui/select';
+
+const ThemeSelector = ({ currentTheme, onThemeChange, t }: any) => {
+  return (
+    <Select value={currentTheme} onValueChange={onThemeChange}>
+      <SelectTrigger className="w-36">
+        <SelectValue />
+      </SelectTrigger>
+      <SelectContent>
+        <SelectItem value="light">{t('themeSelectorLight')}</SelectItem>
+        <SelectItem value="dark">{t('themeSelectorDark')}</SelectItem>
+        <SelectItem value="system">{t('themeSelectorSystem')}</SelectItem>
+      </SelectContent>
+    </Select>
+  );
+};
+
+export default ThemeSelector;