feat(ui): implement Bento Grid design system

- Add Urbanist font (replace Inter)
- Add CSS variables: --bento-radius, --bento-gap, --bento-padding
- Add Tailwind extend: rounded-bento, rounded-4xl, spacing.bento
- Create BentoCard component with size variants (sm/md/lg/xl)
- Add .bento-card, .bento-card-hover, .bento-card-glow classes
- Add .bento-grid container with responsive columns
- Implement floating TabBar (margin 16px, shadow, pill active state)
- Apply bento styles to Dashboard cards
- Support both dark and light themes

src/components/ui/BentoCard.tsx

@@ -0,0 +1,115 @@
+import { Link } from 'react-router-dom'
+import { forwardRef } from 'react'
+
+export type BentoSize = 'sm' | 'md' | 'lg' | 'xl'
+
+interface BentoCardBaseProps {
+  size?: BentoSize
+  children: React.ReactNode
+  className?: string
+  hover?: boolean
+  glow?: boolean
+}
+
+interface BentoCardDivProps extends BentoCardBaseProps {
+  as?: 'div'
+  onClick?: () => void
+}
+
+interface BentoCardLinkProps extends BentoCardBaseProps {
+  as: 'link'
+  to: string
+  state?: unknown
+}
+
+interface BentoCardButtonProps extends BentoCardBaseProps {
+  as: 'button'
+  onClick?: () => void
+  disabled?: boolean
+  type?: 'button' | 'submit'
+}
+
+export type BentoCardProps = BentoCardDivProps | BentoCardLinkProps | BentoCardButtonProps
+
+const sizeClasses: Record<BentoSize, string> = {
+  sm: '',
+  md: 'col-span-2',
+  lg: 'row-span-2',
+  xl: 'col-span-2 row-span-2',
+}
+
+const baseClasses = `
+  bento-card
+  rounded-[var(--bento-radius)]
+  p-[var(--bento-padding)]
+  bg-dark-900/70
+  border border-dark-700/40
+  transition-all duration-300 ease-smooth
+`
+
+const hoverClasses = `
+  cursor-pointer
+  hover:bg-dark-800/60
+  hover:border-dark-600/50
+  hover:shadow-lg
+  hover:scale-[1.01]
+  active:scale-[0.99]
+`
+
+const glowClasses = `
+  hover:shadow-glow
+  hover:border-accent-500/30
+`
+
+export const BentoCard = forwardRef<HTMLDivElement, BentoCardProps>((props, ref) => {
+  const { 
+    size = 'sm', 
+    children, 
+    className = '', 
+    hover = false,
+    glow = false,
+  } = props
+
+  const classes = [
+    baseClasses,
+    sizeClasses[size],
+    hover && hoverClasses,
+    glow && glowClasses,
+    className,
+  ].filter(Boolean).join(' ')
+
+  if (props.as === 'link') {
+    const { to, state } = props as BentoCardLinkProps
+    return (
+      <Link to={to} state={state} className={classes}>
+        {children}
+      </Link>
+    )
+  }
+
+  if (props.as === 'button') {
+    const { onClick, disabled, type = 'button' } = props as BentoCardButtonProps
+    return (
+      <button
+        ref={ref as React.Ref<HTMLButtonElement>}
+        type={type}
+        onClick={onClick}
+        disabled={disabled}
+        className={classes}
+      >
+        {children}
+      </button>
+    )
+  }
+
+  const { onClick } = props as BentoCardDivProps
+  return (
+    <div ref={ref} onClick={onClick} className={classes}>
+      {children}
+    </div>
+  )
+})
+
+BentoCard.displayName = 'BentoCard'
+
+export default BentoCard