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/layout/Sidebar.tsx

@@ -0,0 +1,54 @@
+import React from 'react';
+import { Link } from 'react-router-dom';
+import { PanelLeft, PanelLeftClose, Package } from 'lucide-react';
+import { useActiveSection } from '@/hooks/useActiveSection';
+import { __ } from '@/lib/i18n';
+import { iconMap } from '@/lib/nav-icons';
+
+interface SidebarProps {
+  collapsed: boolean;
+  onToggle: () => void;
+}
+
+export function Sidebar({ collapsed, onToggle }: SidebarProps) {
+  const link = "flex items-center gap-2 rounded-md px-3 py-2 hover:bg-accent hover:text-accent-foreground shadow-none hover:shadow-none focus:shadow-none focus:outline-none focus:ring-0 transition-all";
+  const linkCollapsed = "flex items-center justify-center rounded-md p-2 hover:bg-accent hover:text-accent-foreground shadow-none hover:shadow-none focus:shadow-none focus:outline-none focus:ring-0 transition-all";
+  const active = "bg-secondary";
+  const { main } = useActiveSection();
+
+  // Get navigation tree from backend
+  const navTree = window.WNW_NAV_TREE || [];
+
+  return (
+    <aside className={`flex-shrink-0 border-r border-border sticky top-16 h-[calc(100vh-64px)] overflow-y-auto bg-background flex flex-col transition-all duration-200 ${collapsed ? 'w-14' : 'w-56'}`}>
+      {/* Toggle button */}
+      <div className={`p-2 border-b border-border ${collapsed ? 'flex justify-center' : 'flex justify-end'}`}>
+        <button
+          onClick={onToggle}
+          className="p-2 rounded-md hover:bg-accent hover:text-accent-foreground transition-colors"
+          title={collapsed ? __('Expand sidebar') : __('Collapse sidebar')}
+        >
+          {collapsed ? <PanelLeft className="w-4 h-4" /> : <PanelLeftClose className="w-4 h-4" />}
+        </button>
+      </div>
+
+      <nav className={`flex flex-col gap-1 flex-1 ${collapsed ? 'p-1' : 'p-3'}`}>
+        {navTree.map((item: any) => {
+          const IconComponent = iconMap[item.icon] || Package;
+          const isActive = main.key === item.key;
+          return (
+            <Link
+              key={item.key}
+              to={item.path}
+              className={`${collapsed ? linkCollapsed : link} ${isActive ? active : ''}`}
+              title={collapsed ? item.label : undefined}
+            >
+              <IconComponent className="w-4 h-4 flex-shrink-0" />
+              {!collapsed && <span>{item.label}</span>}
+            </Link>
+          );
+        })}
+      </nav>
+    </aside>
+  );
+}