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/blueprints/fields/og-image.php

@@ -0,0 +1,31 @@
+<?php
+
+use Kirby\Cms\App;
+use Kirby\Toolkit\Str;
+
+return function (App $kirby) {
+	$blueprint = [
+		'type' => 'files',
+		'multiple' => false,
+		'uploads' => [],
+		'query' => 'model.images'
+	];
+
+	if ($parent = option('tobimori.seo.files.parent')) {
+		$blueprint['uploads'] = [
+			'parent' => $parent
+		];
+		$blueprint['query'] = "{$parent}.images";
+	}
+
+	if ($template = option('tobimori.seo.files.template')) {
+		$blueprint['uploads'] = [
+			...$blueprint['uploads'],
+			'template' => $template
+		];
+
+		$blueprint['query'] = "{$blueprint['query']}.filterBy('template', '{$template}')";
+	}
+
+	return $blueprint;
+};