Update project title and enhance dark mode styling

- Changed project title from "RAG Chat" to "Quick Understand" in App and Chat components for improved clarity.
- Added darker background styling for headers in dark mode to enhance visual consistency and user experience.

app/frontend/src/App.js

@@ -77,11 +77,11 @@ function App() {
   return (
     <ThemeProvider defaultTheme="light">
       <div className="min-h-screen bg-background text-foreground transition-colors duration-300 flex flex-col">
-        <header className="bg-primary text-primary-foreground py-4 px-6 shadow-md w-full">
+        <header className="bg-primary text-primary-foreground py-4 px-6 shadow-md w-full dark:bg-gray-900">
           <div className="container mx-auto flex items-center justify-between">
             <div className="flex items-center gap-2">
               <span role="img" aria-label="brain" className="text-2xl">🧠</span>
-              <h1 className="text-2xl font-bold">RAG Chat</h1>
+              <h1 className="text-2xl font-bold">Quick Understand</h1>
             </div>
             <div className="flex items-center gap-4">
               {!showUploadForm && uploadedFiles.length > 0 && (

app/frontend/src/components/Chat.js

@@ -490,7 +490,7 @@ ${results.score >= 80
             <div className="mb-4 rounded-full bg-primary/10 p-6 transition-all duration-300">
               <span role="img" aria-label="chat" className="text-4xl">💬</span>
             </div>
-            <h3 className="mb-2 text-xl font-semibold">Welcome to the RAG Chat!</h3>
+            <h3 className="mb-2 text-xl font-semibold">Welcome to Quick Understand!</h3>
             <p className="text-sm text-muted-foreground max-w-md">
               Ask questions about your document or click one of the suggested questions above.
               I'm here to help you understand the content! ✨

app/frontend/src/globals.css

@@ -306,4 +306,13 @@ button, a {
   color: hsl(var(--primary));
   transform: scale(1.1);
   z-index: 1;
+}
+
+/* Add a darker header background for dark mode */
+.dark .markdown-content h1,
+.dark .markdown-content h2,
+.dark .markdown-content h3,
+.dark .markdown-content h4 {
+  background-color: hsl(var(--primary));
+  color: hsl(var(--primary-foreground));
 }