style(components): refine core UI components for minimal aesthetics

- card: switched to subtle borders (border-white/5)
- input: increased height to h-10, enhanced focus transitions, removed internal shadows
- button: removed default shadows for flatter appearance

src/components/ui/input.tsx

@@ -9,7 +9,7 @@ const Input = React.forwardRef<HTMLInputElement, InputProps>(
       <input
         type={type}
         className={cn(
-          'border-input placeholder:text-muted-foreground focus-visible:ring-ring flex h-9 w-full rounded-md border bg-transparent px-3 py-1 text-sm shadow-sm transition-colors file:border-0 file:bg-transparent file:text-sm file:font-medium focus-visible:ring-1 focus-visible:outline-none disabled:cursor-not-allowed disabled:opacity-50',
+          'border-input placeholder:text-muted-foreground focus-visible:ring-ring focus-visible:border-primary flex h-10 w-full rounded-md border bg-background px-3 py-2 text-sm transition-colors file:border-0 file:bg-transparent file:text-sm file:font-medium focus-visible:outline-none disabled:cursor-not-allowed disabled:opacity-50',
           className,
         )}
         ref={ref}