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/config/options/indexnow.php

@@ -0,0 +1,29 @@
+<?php
+
+return [
+	'enabled' => true,
+	'searchEngine' => 'https://api.indexnow.org', // one will propagate to all others. so this is fine @see https://www.indexnow.org/faq
+	'rules' => [
+		// by default, only the current page is requested to be indexed (if indexable: robots allow + listed status)
+		// however you might want to index other pages as well. for example, the 'blog overview' page should always be reindexed when a new 'blog post' is indexed
+		//
+		// syntax: 'match pattern' => ['invalidation rules']
+		//
+		// match patterns:
+		// - '/blog/*' - url pattern (glob or regex)
+		// - 'article' - template name
+		// - '*' - wildcard, matches all pages
+		//
+		// invalidation rules:
+		// - 'parent' => true (direct parent) or number (levels up)
+		// - 'children' => true (all descendants) or number (depth limit)
+		// - 'siblings' => true (all siblings at same level)
+		// - 'urls' => ['/shop', '/'] (specific urls to invalidate)
+		// - 'templates' => ['category', 'shop'] (invalidate all pages with these templates)
+		//
+		// examples:
+		// '/blog/*' => ['parent' => true],
+		// 'article' => ['parent' => 2, 'urls' => ['/blog', '/']],
+		// 'product' => ['parent' => true, 'siblings' => true, 'templates' => ['category']],
+	],
+];