feat: optimize chat page scroll area

packages/client/ui-primitives/src/markdown/CodeBlock.module.css

@@ -74,6 +74,10 @@
   white-space: pre-wrap;
   word-break: break-all;
   background: var(--dsw-alias-markdown-code-block);
+  /* Bottom radii live on <pre>: overflow:hidden on .block would kill the
+     sticky banner, and this opaque fill otherwise squares off the wrapper. */
+  border-bottom-left-radius: var(--dsl-code-block-border-radius);
+  border-bottom-right-radius: var(--dsl-code-block-border-radius);
 }
 
 /* Shiki inlines its theme background var; route it to the repo token. */