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

static/css/custom.css

@@ -15,6 +15,7 @@ pre, code {
 hr.small {
   border-width: 5px;
   border-color: #00a185;
+  margin-top: 4rem;
 }
 
 h1,h2,h3,h4,h5,h6 {
@@ -129,6 +130,19 @@ footer .copyright {
   font-family: "Linux Biolinum O", 'Helvetica Neue', Helvetica, Arial, sans-serif;
 }
 
+.thumbApps {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 12px;
+    margin-bottom: 20px;
+}
+
+.thumbApps > a {
+    flex: 1 1 180px;
+    min-width: 0;
+    text-decoration: none;
+}
+
 .thumbApp {
     background-position: 50% 50%;
     background-repeat: no-repeat;
@@ -137,18 +151,14 @@ footer .copyright {
     box-shadow: 0px 0px 10px #555;
     font-family: "Linux Biolinum O", 'Helvetica Neue', Helvetica, Arial, sans-serif;
     height: 200px;
-    display: block;
-    float: left;
-    margin-right: 0.5%;
-    margin-bottom: 20px;
-    width: 24.5%;
-    min-width: 149px;
+    display: flex;
+    flex-direction: column;
+    justify-content: flex-end;
+    transition: transform 0.2s ease, box-shadow 0.2s ease;
 }
-
-@media only screen and (max-width: 330px) {
-    .thumbApp {
-        min-width: 100%;
-    }
+.thumbApps > a:hover .thumbApp {
+    transform: translateY(-4px) scale(1.02);
+    box-shadow: 0px 8px 20px #444;
 }
 @media only screen and (max-width: 850px) {
     .avatar-container {
@@ -164,9 +174,10 @@ footer .copyright {
 .thumbApp p {
     background-color: rgba(0,0,0,0.7);
     border-bottom: solid 4px #00a185;
+    border-radius: 0 0 0 1px;
     color: white;
     font-weight: bolder;
-    margin-top: 123px;
+    margin: 0;
     padding: 10px;
 }
 .thumbApp:hover p {