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

layouts/partials/header.html

@@ -90,14 +90,15 @@
 
     {{ if $thumbs }}
     <div class="container">
-      {{range $i, $thumb := $thumbs}}
-      <a href="{{ $thumb.link | absURL }}" target="_blank">
-        <div class="thumbApp" style="background-image:url('{{ $thumb.src | absURL }}')">
-          {{ if $thumb.desc }}<p><span>{{ $thumb.desc }}</span></p>{{end}}
-        </div>
-      </a>
-      {{ end }}
-      <span style="clear:both; display: block"></span>
+      <div class="thumbApps">
+        {{range $i, $thumb := $thumbs}}
+        <a href="{{ $thumb.link | absURL }}" target="_blank">
+          <div class="thumbApp" style="background-image:url('{{ $thumb.src | absURL }}')">
+            {{ if $thumb.desc }}<p><span>{{ $thumb.desc }}</span></p>{{end}}
+          </div>
+        </a>
+        {{ end }}
+      </div>
       <hr class="small">
     </div>
     {{ end }}