feat: P1 滚动到底部浮动按钮

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

langgraph/src/main.tsx

@@ -564,21 +564,21 @@ function App() {
               ))}
 
           <div ref={bottomRef} />
-        </div>
 
-        {/* Scroll-to-bottom floating button */}
-        {showScrollBtn && (
-          <div className="absolute bottom-32 left-1/2 -translate-x-1/2 z-10">
-            <button
-              type="button"
-              onClick={() => bottomRef.current?.scrollIntoView({ behavior: "smooth" })}
-              className="rounded-full bg-background border border-border shadow-md p-2 text-muted-foreground hover:text-foreground hover:bg-accent transition-colors"
-              title="滚动到底部"
-            >
-              <ChevronDown className="size-4" />
-            </button>
-          </div>
-        )}
+          {/* Scroll-to-bottom floating button */}
+          {showScrollBtn && (
+            <div className="sticky bottom-4 flex justify-end pr-4 pointer-events-none">
+              <button
+                type="button"
+                onClick={() => bottomRef.current?.scrollIntoView({ behavior: "smooth" })}
+                className="pointer-events-auto rounded-full bg-background/80 backdrop-blur border border-border shadow-md p-2 text-muted-foreground hover:text-foreground hover:bg-accent transition-colors"
+                title="滚动到底部"
+              >
+                <ChevronDown className="size-4" />
+              </button>
+            </div>
+          )}
+        </div>
 
         {/* Control bar: tools (left) + model selector (right) */}
         <div className="shrink-0 border-t border-border px-4 pt-3 pb-0 flex items-center justify-between max-w-3xl mx-auto w-full">