前端功能基本完成

frontend/src/App.tsx

@@ -57,7 +57,9 @@ function App() {
     setSelectedBody(body);
   };
 
-  if (loading) {
+  // Only show full screen loading when we have no data
+  // This prevents flashing when timeline is playing and fetching new data
+  if (loading && bodies.length === 0) {
     return <Loading />;
   }
 

frontend/src/components/TimelineController.tsx

@@ -143,6 +143,7 @@ export function TimelineController({ onTimeChange, minDate, maxDate }: TimelineC
       <div className="flex items-center justify-center gap-4">
         {/* Play/Pause button */}
         <button
+          type="button"
           onClick={handlePlayPause}
           className="bg-blue-600 hover:bg-blue-700 text-white px-4 py-2 rounded"
         >
@@ -166,6 +167,7 @@ export function TimelineController({ onTimeChange, minDate, maxDate }: TimelineC
 
         {/* Reset button */}
         <button
+          type="button"
           onClick={() => {
             setCurrentDate(new Date(startDate)); // Reset to start (now)
             setIsPlaying(false);