Let the dataset description use the full width

The description at the top of both tabs was capped at 860px, leaving an empty band on the right. It now spans the same width as the content below it (1,110px at a 1400px window, measured against the search row).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

app.css

@@ -85,7 +85,8 @@
 /* What was annotated and how: a lead and a closed disclosure at the top of
    both tabs, aligned with the content padding below it. */
 .gradio-container .tab-intro { padding:22px 20px 0; gap:8px; background:transparent; border:0; }
-.gradio-container .tab-intro-lead, .gradio-container .tab-intro-lead p { font:15px/1.65 Arial,Helvetica,sans-serif; color:#33503f; max-width:860px; margin:0; }
+.gradio-container .tab-intro-lead, .gradio-container .tab-intro-lead p { font:15px/1.65 Arial,Helvetica,sans-serif; color:#33503f; max-width:none; margin:0; }
+.gradio-container .tab-intro-lead .prose, .gradio-container .tab-intro-lead .md { max-width:none; }
 .gradio-container .tab-intro .atlas-disclosure { margin-top:4px; }
 #atlas-overview .tab-intro + * .atlas, #atlas-overview .atlas { padding-top:8px; }
 .gradio-container .tab-intro .atlas-disclosure ul { padding-left:22px; margin:6px 0 0; list-style:disc; }