feat: Page Editor v1.0 - canonical schema, SSR parity, and migration

Major improvements to WooNooW Page Editor system:

Schema & Architecture:
- Canonical section schema with unified sectionSchema.ts
- Normalized feature-grid to use items (not features)
- Standardized default values across all section types
- Schema versioning with automatic migration on read

Backend (PHP):
- Enhanced PlaceholderRenderer with typed output contracts
- Added fallback behavior for empty/invalid dynamic sources
- Added caching support for post data resolution
- New SchemaMigration class for backward compatibility
- New Features class for feature flags
- Enhanced PageSSR with full style support
- Removed controller-level special-casing for related_posts

Frontend (Admin SPA):
- Updated CanvasRenderer with schema-aware transformation
- Enhanced InspectorPanel with canonical schema metadata
- Added new section renderers

Frontend (Customer SPA):
- New section components: BentoCategoryGrid, MarqueeBanner, ProductCarousel, ShoppableImage
- Updated FeatureGridSection for items prop contract

Testing:
- Add PHP tests: SchemaMigrationTest, PlaceholderRendererTest, PageSSRTest
- Add TypeScript tests: schema-integration, feature-grid-regression
- Add parity tests for React vs SSR content matching
- Add CI script: check-schema-drift.mjs
- Add VERIFICATION_CHECKLIST.md

Documentation:
- RELEASE_NOTES-v1.0.md with full release notes
- docs/PAGE_EDITOR_SECTION_SCHEMA_V1.md
- docs/PAGE_EDITOR_SSR_COVERAGE_AUDIT.md

admin-spa/src/components/ErrorCard.tsx

@@ -19,18 +19,18 @@ export function ErrorCard({
 }: ErrorCardProps) {
   return (
     <div className="flex items-center justify-center p-8">
-      <div className="max-w-md w-full bg-red-50 border border-red-200 rounded-lg p-6">
+      <div className="max-w-md w-full bg-red-50 dark:bg-red-950/50 border border-red-200 dark:border-red-800 rounded-lg p-6">
         <div className="flex items-start gap-3">
-          <AlertTriangle className="w-5 h-5 text-red-600 flex-shrink-0 mt-0.5" />
+          <AlertTriangle className="w-5 h-5 text-red-600 dark:text-red-400 flex-shrink-0 mt-0.5" />
           <div className="flex-1">
-            <h3 className="font-medium text-red-900">{title}</h3>
+            <h3 className="font-medium text-red-900 dark:text-red-200">{title}</h3>
             {message && (
-              <p className="text-sm text-red-700 mt-1">{message}</p>
+              <p className="text-sm text-red-700 dark:text-red-300 mt-1">{message}</p>
             )}
             {onRetry && (
               <button
                 onClick={onRetry}
-                className="mt-3 inline-flex items-center gap-2 text-sm font-medium text-red-900 hover:text-red-700 transition-colors"
+                className="mt-3 inline-flex items-center gap-2 text-sm font-medium text-red-900 dark:text-red-200 hover:text-red-700 dark:hover:text-red-100 transition-colors"
               >
                 <RefreshCw className="w-4 h-4" />
                 {__('Try again')}
@@ -48,7 +48,7 @@ export function ErrorCard({
  */
 export function ErrorMessage({ message }: { message: string }) {
   return (
-    <div className="flex items-center gap-2 text-sm text-red-600 bg-red-50 border border-red-200 rounded-md p-3">
+    <div className="flex items-center gap-2 text-sm text-red-600 dark:text-red-400 bg-red-50 dark:bg-red-950/50 border border-red-200 dark:border-red-800 rounded-md p-3">
       <AlertTriangle className="w-4 h-4 flex-shrink-0" />
       <span>{message}</span>
     </div>