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/blueprints/pages/default.yml

@@ -1,29 +1,33 @@
 title: Default Page
 
-columns:
-  main:
-    width: 2/3
-    sections:
-      fields:
-        type: fields
-        fields:
-          text:
-            type: writer
-            marks:
-              - bold
-              - italic
-              - green
-              - pixel
-              - underline
-              - strike
-              - clear
-              - link
-  sidebar:
-    width: 1/3
-    sections:
-      pages:
-        type: pages
-        template: default
-      files:
-        type: files
+tabs:
+  content:
+    label: Contenu
+    columns:
+      main:
+        width: 2/3
+        sections:
+          fields:
+            type: fields
+            fields:
+              text:
+                type: writer
+                marks:
+                  - bold
+                  - italic
+                  - green
+                  - pixel
+                  - underline
+                  - strike
+                  - clear
+                  - link
+      sidebar:
+        width: 1/3
+        sections:
+          pages:
+            type: pages
+            template: default
+          files:
+            type: files
 
+  seo: seo/page