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

docs/PAGE_EDITOR_SECTION_SCHEMA_V1.md

@@ -0,0 +1,42 @@
+# Page Editor Section Schema v1
+
+## Purpose
+The Page Editor uses one canonical section contract for editor defaults, inspector fields, canvas rendering, storefront rendering, and PHP SSR expectations.
+
+The TypeScript source of truth is:
+
+```text
+admin-spa/src/routes/Appearance/Pages/schema/sectionSchema.ts
+```
+
+## Canonical Rules
+- Section type names use kebab-case in saved JSON, for example `feature-grid`.
+- Section props are stored as `SectionProp` objects: `{ "type": "static", "value": ... }` or `{ "type": "dynamic", "source": ... }`.
+- Runtime renderers receive flattened prop values after adapter transformation or backend resolution.
+- Repeater props must use arrays as their static value.
+- `feature-grid.items` is the canonical feature/post-card list prop.
+- `feature-grid.features` is supported only as a legacy read fallback.
+
+## Current Section Types
+| Type | Canonical repeater props | Notes |
+|---|---|---|
+| `hero` | none | Dynamic title/subtitle/image supported by inspector metadata |
+| `content` | none | Rich text content may be dynamic |
+| `image-text` | none | Dynamic title/text/image supported |
+| `feature-grid` | `items` | Legacy `features` is read as fallback |
+| `cta-banner` | none | Static CTA content |
+| `contact-form` | none | Webhook/redirect URLs are static settings |
+| `bento-category-grid` | `items` | Array of category/grid item objects |
+| `product-carousel` | none | Product source/limit are scalar props |
+| `shoppable-image` | `hotspots` | Array of product hotspot objects |
+| `marquee-banner` | none | Scalar text/separator/speed props |
+
+## Migration Notes
+- Existing saved `feature-grid.features` values should be read as `items` at render time.
+- New editor writes should persist `feature-grid.items`.
+- A future payload-level `schemaVersion` should make legacy migration explicit.
+
+## Preview Resolution Contract
+- Template preview samples are fetched from `GET /woonoow/v1/preview/samples/{cpt}`.
+- Dynamic template preview sections are resolved through `POST /woonoow/v1/preview/resolve/{cpt}`.
+- The editor must render resolved preview sections separately from the saved source sections so dynamic values do not overwrite `{ type: "dynamic", source: "..." }` metadata.