Pad composer bottom so long text doesn't touch buttons

Add pb-2 inside the floating reply editor's scrollable content so the
last line of a long message has breathing room before the action row.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ui/src/components/IssueChatThread.tsx

@@ -2366,7 +2366,7 @@ const IssueChatComposer = forwardRef<IssueChatComposerHandle, IssueChatComposerP
         imageUploadHandler={onImageUpload}
         fileDropTarget="parent"
         bordered={false}
-        contentClassName="max-h-[28dvh] overflow-y-auto pr-1 text-sm scrollbar-auto-hide"
+        contentClassName="max-h-[28dvh] overflow-y-auto pr-1 pb-2 text-sm scrollbar-auto-hide"
       />
 
       {composerHint ? (