Social banner: per-model bp context on the three model card covers

Each checkpoint ships with a different long-context training schedule,
so the cover should reflect the actual context window for THAT model
instead of treating them as a family-level constant:
- Carbon-500M: 49,152 bp
- Carbon-3B: 393,216 bp
- Carbon-8B: 786,432 bp

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

social-banner.html

@@ -623,7 +623,7 @@
               <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>393,216</strong> bp context</li>
+                <li class="banner-spec"><strong>49,152</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>
@@ -695,7 +695,7 @@
               <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>393,216</strong> bp context</li>
+                <li class="banner-spec"><strong>786,432</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>