feat: intégration plugin Kirby SEO

- Ajout de tobimori/kirby-seo via Composer
- snippet('seo/head') dans header.php (remplace les meta manuels)
- snippet('seo/schemas') dans footer.php pour JSON-LD
- Onglet SEO ajouté dans site.yml et tous les blueprints de pages
- Configuration SEO dans config.php (sitemap, robots, canonicalBase TODO)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

site/plugins/kirby-seo/docs/3_reference/1_permissions.md

@@ -0,0 +1,37 @@
+---
+title: Permissions
+intro: Control access to plugin features by user role
+---
+
+Kirby SEO registers permissions that you can restrict per [user role](https://getkirby.com/docs/guide/users/permissions). By default, all permissions are granted.
+
+## Available permissions
+
+| Permission        | Controls                                                                         |
+| ----------------- | -------------------------------------------------------------------------------- |
+| `tobimori.seo.ai` | Access to all AI Assist features: generating, editing, and customizing meta text |
+
+More permissions will be added in future releases.
+
+## Restricting access
+
+Set a permission to `false` in a role's blueprint to deny it:
+
+```yaml
+# site/blueprints/users/editor.yml
+
+title: Editor
+permissions:
+  tobimori.seo:
+    ai: false
+```
+
+You can also deny all current and future permissions at once using a wildcard:
+
+```yaml
+permissions:
+  tobimori.seo:
+    *: false
+```
+
+Users without a permission will not see the corresponding UI elements in the Panel, and API requests will be rejected.