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

tailwind.config.js

@@ -106,7 +106,15 @@ export default {
         },
       },
       fontFamily: {
-        sans: ['Inter', 'system-ui', '-apple-system', 'BlinkMacSystemFont', 'Segoe UI', 'Roboto', 'sans-serif'],
+        sans: ['Urbanist', 'system-ui', '-apple-system', 'BlinkMacSystemFont', 'Segoe UI', 'Roboto', 'sans-serif'],
+      },
+      borderRadius: {
+        'bento': '24px',
+        '4xl': '32px',
+      },
+      spacing: {
+        'bento': '16px',
+        'bento-lg': '24px',
       },
       fontSize: {
         '2xs': ['0.625rem', { lineHeight: '0.875rem' }],