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/sitemap.php

@@ -0,0 +1,55 @@
+<?php
+
+use tobimori\Seo\Sitemap\SitemapIndex;
+use tobimori\Seo\Meta;
+
+return function (SitemapIndex $sitemap) {
+	$exclude = option('tobimori.seo.sitemap.excludeTemplates', []);
+	$pages = site()->index()->filter(fn ($page) => $page->metadata()->robotsIndex()->toBool() && !in_array($page->intendedTemplate()->name(), $exclude));
+
+	if ($group = option('tobimori.seo.sitemap.groupByTemplate')) {
+		$pages = $pages->group('intendedTemplate');
+	}
+
+	if (is_a($pages->first(), 'Kirby\Cms\Page')) {
+		$pages = $pages->group(fn () => 'pages');
+	}
+
+	foreach ($pages as $group) {
+		$index = $sitemap->create($group ? $group->first()->intendedTemplate()->name() : 'pages');
+
+		foreach ($group as $page) {
+			$url = $index->createUrl($page->metadata()->canonicalUrl())
+				->lastmod($page->modified() ?? (int)(date('c')))
+				->changefreq(is_callable($changefreq = option('tobimori.seo.sitemap.changefreq')) ? $changefreq($page) : $changefreq)
+				->priority(is_callable($priority = option('tobimori.seo.sitemap.priority')) ? $priority($page) : $priority);
+
+			if (kirby()->languages()->count() > 1 && kirby()->language() !== null) {
+				$alternates = [];
+				foreach (kirby()->languages() as $language) {
+					// only if this language is translated for this page and exists
+					if ($page->translation($language->code())->exists()) {
+						/*
+						 * Specification: "lists every alternate version of the page, including itself."
+						 * https://developers.google.com/search/docs/specialty/international/localized-versions#sitemap
+						 */
+						$alternates[] =
+							[
+								'hreflang' => Meta::toBCP47($language),
+								'href' => $page->url($language->code()),
+							];
+					}
+				}
+
+				// add x-default
+				$alternates[] =
+					[
+						'hreflang' => 'x-default',
+						'href' => $page->indexUrl(),
+					];
+
+				$url->alternates($alternates);
+			}
+		}
+	}
+};