Social banner: bump live hero + OG share thumb to Carbon-3B's real 393,216 bp context

Both the animated stage at the top of /social-banner and the static
1200×630 share thumbnail below carry the huggingfacebio/carbon-3b
breadcrumb, but their spec row still read 49,152 bp context — a
stale number from before the long-context training schedule landed.

Bumps them to 393,216 bp to match what demo.html and the Carbon-3B
model-card cover already advertise. The Carbon-500M (49,152) and
Carbon-8B (786,432) model-card covers are left as-is — their numbers
are correct per-checkpoint and intentionally differentiated.

Co-authored-by: Cursor <cursoragent@cursor.com>

social-banner.html

@@ -441,7 +441,7 @@
           <h1 class="banner-wordmark"><span>CARBON</span><span class="banner-cursor" aria-hidden="true"></span></h1>
           <p class="banner-subtitle">Autoregressive Genomic Foundation Model</p>
           <ul class="banner-specs" aria-label="Model specs">
-            <li class="banner-spec"><strong>49,152</strong> bp context</li>
+            <li class="banner-spec"><strong>393,216</strong> bp context</li>
             <li class="banner-spec"><strong>6-mer</strong> tokenizer</li>
             <li class="banner-spec"><strong>1T</strong> train tokens</li>
           </ul>
@@ -569,7 +569,7 @@
               <h1 class="banner-wordmark"><span>CARBON</span><span class="banner-cursor" aria-hidden="true"></span></h1>
               <p class="banner-subtitle">Autoregressive Genomic Foundation Model</p>
               <ul class="banner-specs" aria-label="Model specs">
-                <li class="banner-spec"><strong>49,152</strong> bp context</li>
+                <li class="banner-spec"><strong>393,216</strong> bp context</li>
                 <li class="banner-spec"><strong>6-mer</strong> tokenizer</li>
                 <li class="banner-spec"><strong>1T</strong> train tokens</li>
               </ul>