feat: refactor theme, add tailwind-scrollbar, and improve UI components

- Removed manual theme switching logic and ThemeProvider
- Installed and configured tailwind-scrollbar plugin
- Updated FileConverter and ConversionOptions to use shadcn Input
- Refactored FontSelector to use shadcn Tabs
- Simplified global styles and adjusted glassmorphic effects

components/providers/Providers.tsx

@@ -3,7 +3,6 @@
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
 import { Toaster } from 'sonner';
 import { useState } from 'react';
-import { ThemeProvider } from './ThemeProvider';
 import { TooltipProvider } from '@/components/ui/tooltip';
 import { SWRegistration } from './SWRegistration';
 
@@ -21,14 +20,12 @@ export function Providers({ children }: { children: React.ReactNode }) {
   );
 
   return (
-    <ThemeProvider>
-      <QueryClientProvider client={queryClient}>
-        <TooltipProvider>
-          <SWRegistration />
-          {children}
-        </TooltipProvider>
-        <Toaster position="top-right" richColors />
-      </QueryClientProvider>
-    </ThemeProvider>
+    <QueryClientProvider client={queryClient}>
+      <TooltipProvider>
+        <SWRegistration />
+        {children}
+      </TooltipProvider>
+      <Toaster position="top-right" richColors />
+    </QueryClientProvider>
   );
 }