Add SEO improvements: canonical, hreflang, schema fixes, robots.txt

- Fix breadcrumb schema position bug (3 → 2) for Google Rich Results
- Override article/post schemas to use post image instead of site logo
- Fix og:type to emit "article" on post pages with published/modified times
- Add canonical link and hreflang alternate tags (incl. x-default) for bilingual site
- Add organizationName/organizationLogo params for valid Organization schema
- Add robots.txt with sitemap pointer
- Add preconnect hint for analytics host

config.yml

@@ -28,6 +28,9 @@ params:
       desc: "My school: Épita."
       link: "http://epita.fr/"
 
+  organizationName: "nemunaire's blog"
+  organizationLogo: "https://www.nemunai.re/img/mug.jpg"
+
   author:
     name: "nemunaire"
     email: "blog@nemunai.re"