feat: add design tokens as CSS custom properties

Create src/styles/tokens.css with complete design token system including:
- Surface, text, accent, code, border, focus colors
- State colors (success, warning, error, info)
- Shadow definitions
- Typography families with full fallback stacks
- Typography scale (xs through 3xl) and line heights
- Spacing scale (0 through 12)
- Border radius tokens
- Layout constraints (prose, code, container widths)
- Motion tokens with reduced-motion media query

All values sourced from .design/specs/design-tokens-2026-05-26.md.
Includes verification test with 56 assertions across all categories.

src/styles/tokens.css

@@ -0,0 +1,120 @@
+:root {
+  /* Surfaces */
+  --surface-base: #F5F0E8;
+  --surface-card: #FEFCF7;
+  --surface-code: #EEEAE2;
+  --surface-inset: #E8E3DA;
+
+  /* Text */
+  --text-primary: #2B2421;
+  --text-secondary: #6B5F55;
+  --text-tertiary: #948880;
+
+  /* Accents */
+  --accent-primary: #A0522D;
+  --accent-primary-hover: #8B4726;
+  --accent-secondary: #7D6C2F;
+  --accent-secondary-hover: #6B5C28;
+
+  /* Code */
+  --code-text: #3D342E;
+
+  /* Borders */
+  --border-subtle: #DDD7CD;
+  --border-default: #C2BAA9;
+  --border-strong: #8E857A;
+
+  /* Focus */
+  --focus-ring: #A0522D;
+
+  /* State: Success */
+  --success-bg: #E8EDDF;
+  --success-text: #4A5E3A;
+  --success-border: #B5C4A0;
+
+  /* State: Warning */
+  --warning-bg: #F2E8D0;
+  --warning-text: #7A5C1F;
+  --warning-border: #D4BC7C;
+
+  /* State: Error */
+  --error-bg: #F2DED6;
+  --error-text: #8B3A2A;
+  --error-border: #CFA090;
+
+  /* State: Info */
+  --info-bg: #E5E2DA;
+  --info-text: #4A4540;
+  --info-border: #B8B2A8;
+
+  /* Shadows */
+  --shadow-sm: 0 1px 3px rgba(43, 36, 33, 0.04);
+  --shadow-md: 0 2px 8px rgba(43, 36, 33, 0.06);
+
+  /* Typography families */
+  --font-prose: 'Source Serif 4', 'Source Serif Pro', Georgia, 'Times New Roman', serif;
+  --font-structure: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
+  --font-evidence: 'JetBrains Mono', 'Fira Code', 'SF Mono', Consolas, monospace;
+
+  /* Typography scale */
+  --type-xs: 0.75rem;
+  --type-sm: 0.875rem;
+  --type-base: 1.125rem;
+  --type-lg: 1.375rem;
+  --type-xl: 1.75rem;
+  --type-2xl: 2.25rem;
+  --type-3xl: 2.75rem;
+
+  /* Line heights */
+  --leading-tight: 1.15;
+  --leading-snug: 1.25;
+  --leading-heading: 1.35;
+  --leading-normal: 1.5;
+  --leading-relaxed: 1.6;
+  --leading-prose: 1.7;
+
+  /* Spacing */
+  --space-0: 0;
+  --space-px: 1px;
+  --space-0-5: 0.25rem;
+  --space-1: 0.5rem;
+  --space-1-5: 0.75rem;
+  --space-2: 1rem;
+  --space-2-5: 1.25rem;
+  --space-3: 1.5rem;
+  --space-4: 2rem;
+  --space-5: 2.5rem;
+  --space-6: 3rem;
+  --space-8: 4rem;
+  --space-10: 5rem;
+  --space-12: 6rem;
+
+  /* Border radius */
+  --rounded-none: 0;
+  --rounded-sm: 2px;
+  --rounded-md: 4px;
+  --rounded-lg: 6px;
+  --rounded-xl: 8px;
+  --rounded-full: 9999px;
+
+  /* Layout */
+  --width-prose: 45rem;
+  --width-code: 52.5rem;
+  --width-container: 68.75rem;
+  --gutter: 1.5rem;
+
+  /* Motion */
+  --duration-fast: 100ms;
+  --duration-normal: 150ms;
+  --duration-slow: 250ms;
+  --ease-default: cubic-bezier(0.25, 0.1, 0.25, 1.0);
+  --ease-in-out: cubic-bezier(0.45, 0.05, 0.55, 0.95);
+}
+
+@media (prefers-reduced-motion: reduce) {
+  :root {
+    --duration-fast: 0ms;
+    --duration-normal: 0ms;
+    --duration-slow: 0ms;
+  }
+}

tests/verify-tokens.mjs

@@ -0,0 +1,167 @@
+/**
+ * Verification test for Design Tokens CSS (Task 2)
+ *
+ * Checks that:
+ * 1. src/styles/tokens.css exists
+ * 2. Contains :root block with all token categories
+ * 3. Has ~60-70 CSS custom properties
+ * 4. Includes reduced motion media query
+ * 5. All expected token categories are present
+ */
+import { readFileSync, existsSync } from 'fs';
+import { join, dirname } from 'path';
+import { fileURLToPath } from 'url';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const root = join(__dirname, '..');
+
+let passed = 0;
+let failed = 0;
+
+function assert(condition, message) {
+  if (condition) {
+    console.log(`  ✓ ${message}`);
+    passed++;
+  } else {
+    console.error(`  ✗ ${message}`);
+    failed++;
+  }
+}
+
+function readText(path) {
+  return readFileSync(path, 'utf8');
+}
+
+const tokensPath = join(root, 'src/styles/tokens.css');
+
+// === 1. File exists ===
+console.log('\n1. tokens.css exists');
+assert(existsSync(tokensPath), 'src/styles/tokens.css exists');
+
+if (!existsSync(tokensPath)) {
+  console.log('\nFile not found, skipping remaining tests.');
+  console.log(`\n${'='.repeat(40)}`);
+  console.log(`Results: ${passed} passed, ${failed} failed out of ${passed + failed}`);
+  process.exit(1);
+}
+
+const css = readText(tokensPath);
+
+// === 2. Contains :root block ===
+console.log('\n2. :root block');
+assert(css.includes(':root {'), 'contains :root { block');
+
+// === 3. Token count ~60-70 ===
+console.log('\n3. Custom property count');
+const propertyMatches = css.match(/--[\w-]+\s*:/g);
+const totalProps = propertyMatches ? propertyMatches.length : 0;
+// Inside :root only (exclude media query overrides)
+const rootBlock = css.match(/:root\s*\{([^}]*)\}/);
+const rootContent = rootBlock ? rootBlock[1] : '';
+const rootProps = rootContent.match(/--[\w-]+\s*:/g);
+const rootPropCount = rootProps ? rootProps.length : 0;
+assert(rootPropCount >= 55 && rootPropCount <= 75, `root has ~60-70 custom properties (found ${rootPropCount})`);
+
+// === 4. Surface tokens ===
+console.log('\n4. Surface tokens');
+assert(css.includes('--surface-base: #F5F0E8'), '--surface-base: #F5F0E8');
+assert(css.includes('--surface-card: #FEFCF7'), '--surface-card: #FEFCF7');
+assert(css.includes('--surface-code: #EEEAE2'), '--surface-code: #EEEAE2');
+assert(css.includes('--surface-inset: #E8E3DA'), '--surface-inset: #E8E3DA');
+
+// === 5. Text tokens ===
+console.log('\n5. Text tokens');
+assert(css.includes('--text-primary: #2B2421'), '--text-primary');
+assert(css.includes('--text-secondary: #6B5F55'), '--text-secondary');
+assert(css.includes('--text-tertiary: #948880'), '--text-tertiary');
+
+// === 6. Accent tokens ===
+console.log('\n6. Accent tokens');
+assert(css.includes('--accent-primary: #A0522D'), '--accent-primary');
+assert(css.includes('--accent-primary-hover: #8B4726'), '--accent-primary-hover');
+assert(css.includes('--accent-secondary: #7D6C2F'), '--accent-secondary');
+assert(css.includes('--accent-secondary-hover: #6B5C28'), '--accent-secondary-hover');
+
+// === 7. Code token ===
+console.log('\n7. Code token');
+assert(css.includes('--code-text: #3D342E'), '--code-text');
+
+// === 8. Border tokens ===
+console.log('\n8. Border tokens');
+assert(css.includes('--border-subtle: #DDD7CD'), '--border-subtle');
+assert(css.includes('--border-default: #C2BAA9'), '--border-default');
+assert(css.includes('--border-strong: #8E857A'), '--border-strong');
+
+// === 9. Focus token ===
+console.log('\n9. Focus token');
+assert(css.includes('--focus-ring: #A0522D'), '--focus-ring');
+
+// === 10. State tokens ===
+console.log('\n10. State tokens');
+assert(css.includes('--success-bg:'), 'success-bg');
+assert(css.includes('--success-text:'), 'success-text');
+assert(css.includes('--success-border:'), 'success-border');
+assert(css.includes('--warning-bg:'), 'warning-bg');
+assert(css.includes('--warning-text:'), 'warning-text');
+assert(css.includes('--warning-border:'), 'warning-border');
+assert(css.includes('--error-bg:'), 'error-bg');
+assert(css.includes('--error-text:'), 'error-text');
+assert(css.includes('--error-border:'), 'error-border');
+assert(css.includes('--info-bg:'), 'info-bg');
+assert(css.includes('--info-text:'), 'info-text');
+assert(css.includes('--info-border:'), 'info-border');
+
+// === 11. Shadow tokens ===
+console.log('\n11. Shadow tokens');
+assert(css.includes('--shadow-sm:'), '--shadow-sm');
+assert(css.includes('--shadow-md:'), '--shadow-md');
+
+// === 12. Typography family tokens ===
+console.log('\n12. Typography family tokens');
+assert(css.includes('--font-prose:') && css.includes('Source Serif 4'), '--font-prose with Source Serif 4');
+assert(css.includes('--font-structure:') && css.includes('Inter'), '--font-structure with Inter');
+assert(css.includes('--font-evidence:') && css.includes('JetBrains Mono'), '--font-evidence with JetBrains Mono');
+
+// === 13. Spacing tokens ===
+console.log('\n13. Spacing tokens');
+assert(css.includes('--space-0:'), '--space-0');
+assert(css.includes('--space-1:'), '--space-1');
+assert(css.includes('--space-4:'), '--space-4');
+assert(css.includes('--space-12:'), '--space-12');
+
+// === 14. Border radius tokens ===
+console.log('\n14. Border radius tokens');
+assert(css.includes('--rounded-none:'), '--rounded-none');
+assert(css.includes('--rounded-sm:'), '--rounded-sm');
+assert(css.includes('--rounded-full:'), '--rounded-full');
+
+// === 15. Layout tokens ===
+console.log('\n15. Layout tokens');
+assert(css.includes('--width-prose: 45rem'), '--width-prose');
+assert(css.includes('--width-code: 52.5rem'), '--width-code');
+assert(css.includes('--width-container: 68.75rem'), '--width-container');
+assert(css.includes('--gutter: 1.5rem'), '--gutter');
+
+// === 16. Motion tokens ===
+console.log('\n16. Motion tokens');
+assert(css.includes('--duration-fast:'), '--duration-fast');
+assert(css.includes('--duration-normal:'), '--duration-normal');
+assert(css.includes('--duration-slow:'), '--duration-slow');
+assert(css.includes('--ease-default:'), '--ease-default');
+assert(css.includes('--ease-in-out:'), '--ease-in-out');
+
+// === 17. Reduced motion media query ===
+console.log('\n17. Reduced motion media query');
+assert(css.includes('prefers-reduced-motion: reduce'), 'has prefers-reduced-motion media query');
+assert(css.includes('--duration-fast: 0ms'), 'duration-fast zeroed in reduced motion');
+assert(css.includes('--duration-normal: 0ms'), 'duration-normal zeroed in reduced motion');
+assert(css.includes('--duration-slow: 0ms'), 'duration-slow zeroed in reduced motion');
+
+// === Summary ===
+console.log(`\n${'='.repeat(40)}`);
+console.log(`Results: ${passed} passed, ${failed} failed out of ${passed + failed}`);
+if (failed > 0) {
+  process.exit(1);
+} else {
+  console.log('All token verification tests passed!');
+}