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/GitCloneButton.tsx

@@ -156,13 +156,13 @@ ${escapeBoltTags(file.content)}
       <Button
         onClick={() => setIsDialogOpen(true)}
         title="Clone a Git Repo"
-        variant="outline"
+        variant="default"
         size="lg"
         className={classNames(
           'gap-2 bg-bolt-elements-background-depth-1',
           'text-bolt-elements-textPrimary',
           'hover:bg-bolt-elements-background-depth-2',
-          'border-[rgba(0,0,0,0.08)] dark:border-[rgba(255,255,255,0.08)]',
+          'border border-bolt-elements-borderColor',
           'h-10 px-4 py-2 min-w-[120px] justify-center',
           'transition-all duration-200 ease-in-out',
           className,