Add Site Metadata Endpoint and API Key Management

- Introduced a new Site Metadata endpoint (`GET /wp-json/igny8/v1/site-metadata/`) for retrieving available post types and taxonomies, including counts.
- Added API key input in the admin settings for authentication, with secure storage and revocation functionality.
- Implemented a toggle for enabling/disabling two-way sync operations.
- Updated documentation to reflect new features and usage examples.
- Enhanced permission checks for REST API calls to ensure secure access.

igny8-wp-integration-plugin/README.md

@@ -249,6 +249,35 @@ $result = $integration->full_site_scan();
 - `igny8_send_site_data_to_igny8($site_id)` - Send site data to IGNY8
 - `igny8_map_site_to_semantic_strategy($site_id, $site_data)` - Map to semantic structure
 
+### Site Metadata Endpoint (Plugin)
+
+The plugin exposes a discovery endpoint that your IGNY8 app can call to learn which WordPress post types and taxonomies exist and how many items each contains.
+
+- Endpoint: `GET /wp-json/igny8/v1/site-metadata/`
+- Auth: Plugin-level connection must be enabled and authenticated (plugin accepts stored API key or access token)
+- Response: IGNY8 unified response format (`success`, `data`, `message`, `request_id`)
+
+Example response:
+
+```json
+{
+  "success": true,
+  "data": {
+    "post_types": {
+      "post": { "label": "Posts", "count": 123 },
+      "page": { "label": "Pages", "count": 12 }
+    },
+    "taxonomies": {
+      "category": { "label": "Categories", "count": 25 },
+      "post_tag": { "label": "Tags", "count": 102 }
+    },
+    "generated_at": 1700553600
+  },
+  "message": "Site metadata retrieved",
+  "request_id": "550e8400-e29b-41d4-a716-446655440000"
+}
+```
+
 ---
 
 ## File Structure