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/docs/1_features/02_indexnow.md

@@ -0,0 +1,56 @@
+---
+title: IndexNow
+intro: Notify search engines when your content changes
+---
+
+Normally, search engines discover changes to your site on their own schedule, which can take days or weeks. [IndexNow](https://www.indexnow.org/) lets you skip the wait: whenever you save, publish, or move a page in Kirby, Kirby SEO notifies search engines so they can re-crawl right away.
+
+IndexNow is supported by Bing, Yandex, Seznam, and others. Kirby SEO sends a single request to `api.indexnow.org`, which propagates to all participating search engines. Google does not support IndexNow but is not affected by it.
+
+## How it works
+
+IndexNow is triggered on three events:
+
+- A page is saved
+- A page changes status (e.g. draft to listed)
+- A page's slug changes
+
+Only pages that are listed and not marked as `noindex` are submitted. On local environments (localhost), no requests are sent.
+
+## API key
+
+IndexNow requires an API key to verify that you own the domain. Kirby SEO generates one automatically and caches it permanently. Search engines can verify it at `https://example.com/indexnow-{key}.txt`, which Kirby SEO serves as a route. You don't need to manage this yourself.
+
+## Related URLs
+
+By default, only the changed page itself is submitted. But when a page changes, other pages might be affected too: a blog post's parent archive shows a different excerpt, or sibling pages have updated navigation.
+
+You can configure rules to submit related URLs along with the changed page:
+
+```php
+// site/config/config.php
+return [
+  'tobimori.seo' => [
+    'indexnow' => [
+      'rules' => [
+        // when a blog post changes, also re-index its parent
+        '/blog/*' => ['parent' => true],
+
+        // when an article changes, re-index two levels of parents and specific URLs
+        'article' => ['parent' => 2, 'urls' => ['/blog', '/']],
+
+        // when a product changes, re-index siblings and all category pages
+        'product' => ['parent' => true, 'siblings' => true, 'templates' => ['category']],
+      ],
+    ],
+  ],
+];
+```
+
+Rules match either by URL pattern (`/blog/*`) or by template name (`article`). Each rule can use any combination of:
+
+- `parent`: `true` for the direct parent, or a number for how many levels up
+- `children`: `true` for all descendants, or a number to limit depth
+- `siblings`: `true` to include all pages at the same level
+- `urls`: an array of specific URLs to submit
+- `templates`: an array of template names, all pages with those templates will be submitted