style(chat): update button variants and improve file preview styling

Change button variants from 'outline' to 'default' for consistency across components. Enhance FilePreview component with better spacing, borders, and file name display to improve visual clarity and user experience.

app/components/chat/BaseChat.tsx

@@ -641,23 +641,25 @@ export const BaseChat = React.forwardRef<HTMLDivElement, BaseChatProps>(
                 </div>
               </div>
             </StickToBottom>
-            <div className="flex flex-col justify-center gap-5">
+            <div className="flex flex-col justify-center">
               {!chatStarted && (
                 <div className="flex justify-center gap-2">
                   {ImportButtons(importChat)}
                   <GitCloneButton importChat={importChat} />
                 </div>
               )}
-              {!chatStarted &&
-                ExamplePrompts((event, messageInput) => {
-                  if (isStreaming) {
-                    handleStop?.();
-                    return;
-                  }
+              <div className="flex flex-col gap-5">
+                {!chatStarted &&
+                  ExamplePrompts((event, messageInput) => {
+                    if (isStreaming) {
+                      handleStop?.();
+                      return;
+                    }
 
-                  handleSendMessage?.(event, messageInput);
-                })}
-              {!chatStarted && <StarterTemplates />}
+                    handleSendMessage?.(event, messageInput);
+                  })}
+                {!chatStarted && <StarterTemplates />}
+              </div>
             </div>
           </div>
           <ClientOnly>