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/site-methods.php

@@ -0,0 +1,48 @@
+<?php
+
+use Kirby\Http\Url;
+use Kirby\Toolkit\Str;
+use tobimori\Seo\Seo;
+
+return [
+	'schema' => fn ($type) => Seo::option('components.schema')::getInstance($type),
+	'schemas' => fn () => Seo::option('components.schema')::getInstances(),
+	'lang' => fn () => Seo::option('components.meta')::normalizeLocale(Seo::option('default.locale', args: [$this->homePage()]), '-'),
+	'canonicalFor' => function (string $url, bool $useRootUrl = false) {
+		// Determine the base URL
+		$base = Seo::option('canonical.base', Seo::option('canonicalBase'));
+		if (!$base) {
+			// If useRootUrl is true or this is a multilang site requesting root URL, use kirby()->url()
+			if ($useRootUrl && kirby()->multilang()) {
+				$base = kirby()->url();
+			} else {
+				$base = $this->url();
+			}
+		}
+
+		if (Str::startsWith($url, $base)) {
+			$canonicalUrl = $url;
+		} else {
+			$path = Url::path($url);
+			$canonicalUrl = url($base . '/' . $path);
+		}
+
+		$trailingSlash = Seo::option('canonical.trailingSlash', false);
+		if ($trailingSlash) {
+			// check if URL has a file extension (like .xml, .jpg, .pdf, etc.)
+			$path = parse_url($canonicalUrl, PHP_URL_PATH) ?? '';
+			$pathInfo = pathinfo($path);
+			$hasExtension = !empty($pathInfo['extension'] ?? null);
+
+			// Only add trailing slash if:
+			// - URL doesn't already have one
+			// - URL doesn't have a file extension
+			// - URL isn't just the base domain
+			if (!Str::endsWith($canonicalUrl, '/') && !$hasExtension && $canonicalUrl !== $base) {
+				$canonicalUrl .= '/';
+			}
+		}
+
+		return $canonicalUrl;
+	}
+];