feat(site-builder): per-page SEO meta + favicon + design-token CSS-var wiring + published-output a11y/perf

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/panels/right/SiteDesignPanel.tsx

@@ -1,6 +1,7 @@
 import React, { useState } from 'react';
 import { useSiteDesign, DEFAULT_SITE_DESIGN } from '../../state/SiteDesignContext';
 import { FONT_FAMILIES } from '../../constants/presets';
+import { AssetPicker } from '../../ui/AssetPicker';
 
 type DesignTab = 'basic' | 'advanced';
 
@@ -200,6 +201,19 @@ export const SiteDesignPanel: React.FC = () => {
       {/* Basic tab */}
       {tab === 'basic' && (
         <>
+          <div className="guided-section">
+            <label className="guided-section-label">Favicon</label>
+            <AssetPicker
+              value={design.favicon}
+              onChange={(url) => updateDesign({ favicon: url })}
+              mediaType="image"
+              variant="full"
+              placeholder="Or paste favicon URL..."
+            />
+            <p style={{ fontSize: 10, color: 'var(--color-text-dim)', margin: '4px 0 0' }}>
+              Shown in browser tabs and bookmarks. Applies site-wide.
+            </p>
+          </div>
           <ColorField
             label="Primary Color"
             value={design.primaryColor}