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/button.tsx

@@ -9,12 +9,12 @@ const buttonVariants = cva(
   {
     variants: {
       variant: {
-        default: 'bg-primary text-primary-foreground shadow-xs hover:bg-primary/90',
+        default: 'bg-primary text-primary-foreground shadow-none hover:bg-primary/90',
         destructive:
-          'bg-destructive text-white shadow-xs hover:bg-destructive/90 focus-visible:ring-destructive/20 dark:focus-visible:ring-destructive/40 dark:bg-destructive/60',
+          'bg-destructive text-white shadow-none hover:bg-destructive/90 focus-visible:ring-destructive/20 dark:focus-visible:ring-destructive/40 dark:bg-destructive/60',
         outline:
-          'border bg-background shadow-xs hover:bg-accent hover:text-accent-foreground dark:bg-input/30 dark:border-input dark:hover:bg-input/50',
-        secondary: 'bg-secondary text-secondary-foreground shadow-xs hover:bg-secondary/80',
+          'border bg-background shadow-none hover:bg-accent hover:text-accent-foreground dark:bg-input/30 dark:border-input dark:hover:bg-input/50',
+        secondary: 'bg-secondary text-secondary-foreground shadow-none hover:bg-secondary/80',
         ghost: 'hover:bg-accent hover:text-accent-foreground dark:hover:bg-accent/50',
         link: 'text-primary underline-offset-4 hover:underline',
       },

src/components/ui/card.tsx

@@ -5,7 +5,7 @@ const Card = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElemen
   ({ className, ...props }, ref) => (
     <div
       ref={ref}
-      className={cn('bg-card text-card-foreground rounded-xl border shadow', className)}
+      className={cn('bg-card text-card-foreground rounded-xl border border-white/5 shadow-sm', className)}
       {...props}
     />
   ),

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}