Task 8: Build reusable Card component with CardHeader

- Create Card component with base styling (white bg, 8px radius, shadow-sm)
- Hover state: deepens shadow to shadow-md, strengthens border
- Full-width variant spans both grid columns
- CardHeader sub-component with colored dot, title, optional right text
- Dot colors: teal, amber, green, alert, purple
- Header styling: 12px uppercase title, 10px mono right text
- All styles use CSS custom properties from design tokens

src/components/Card.tsx

@@ -0,0 +1,91 @@
+import React from 'react'
+
+interface CardProps {
+  children: React.ReactNode
+  full?: boolean // spans both grid columns
+  className?: string
+}
+
+export function Card({ children, full, className }: CardProps) {
+  const [isHovered, setIsHovered] = React.useState(false)
+
+  const baseStyles: React.CSSProperties = {
+    background: 'var(--surface)',
+    border: isHovered
+      ? '1px solid var(--border)'
+      : '1px solid var(--border-light)',
+    borderRadius: 'var(--radius)',
+    padding: '20px',
+    boxShadow: isHovered ? 'var(--shadow-md)' : 'var(--shadow-sm)',
+    transition: 'box-shadow 0.2s, border-color 0.2s',
+    gridColumn: full ? '1 / -1' : undefined,
+  }
+
+  return (
+    <div
+      style={baseStyles}
+      className={className}
+      onMouseEnter={() => setIsHovered(true)}
+      onMouseLeave={() => setIsHovered(false)}
+    >
+      {children}
+    </div>
+  )
+}
+
+interface CardHeaderProps {
+  dotColor: 'teal' | 'amber' | 'green' | 'alert' | 'purple'
+  title: string
+  rightText?: string
+}
+
+const dotColorMap: Record<CardHeaderProps['dotColor'], string> = {
+  teal: '#0D6E6E',
+  amber: '#D97706',
+  green: '#059669',
+  alert: '#DC2626',
+  purple: '#7C3AED',
+}
+
+export function CardHeader({ dotColor, title, rightText }: CardHeaderProps) {
+  const headerStyles: React.CSSProperties = {
+    display: 'flex',
+    alignItems: 'center',
+    gap: '8px',
+    marginBottom: '16px',
+  }
+
+  const dotStyles: React.CSSProperties = {
+    width: '8px',
+    height: '8px',
+    borderRadius: '50%',
+    backgroundColor: dotColorMap[dotColor],
+    flexShrink: 0,
+  }
+
+  const titleStyles: React.CSSProperties = {
+    fontSize: '12px',
+    fontWeight: 600,
+    textTransform: 'uppercase',
+    letterSpacing: '0.06em',
+    color: 'var(--text-secondary)',
+  }
+
+  const rightTextStyles: React.CSSProperties = {
+    fontSize: '10px',
+    fontWeight: 400,
+    textTransform: 'none',
+    letterSpacing: 'normal',
+    color: 'var(--text-tertiary)',
+    fontFamily: "'Geist Mono', monospace",
+    marginLeft: 'auto',
+  }
+
+  return (
+    <div style={headerStyles}>
+      <div style={dotStyles} />
+      <span style={titleStyles}>{title}</span>
+      {rightText && <span style={rightTextStyles}>{rightText}</span>}
+    </div>
+  )
+}