Tooltips in the Notebooks chooser

From the development repository at e819bc4.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

client/kokkoja.css

@@ -571,6 +571,7 @@ button.mark.unavailable { opacity: 0.4; }
   color: white;
   font-size: 0.85rem;
   line-height: 1.35;
+  white-space: pre-line;      /* A page card's tooltip has several lines. */
   box-shadow: 0 2px 8px rgb(0 0 0 / 0.25);
   pointer-events: none;
 }