Update voice demo camera drawer

examples/webpage/app.js

@@ -78,6 +78,7 @@ const els = {
   cameraPhoto: document.getElementById("camera-photo"),
   cameraCanvas: document.getElementById("camera-canvas"),
   cameraStartBtn: document.getElementById("camera-start-btn"),
+  cameraDeviceRow: document.getElementById("camera-device-row"),
   cameraDeviceSelect: document.getElementById("camera-device-select"),
   cameraUpload: document.getElementById("camera-upload"),
   cameraSamples: document.getElementById("camera-samples"),
@@ -257,9 +258,6 @@ function syncCameraDrawer(value) {
     els.cameraQuestion.textContent = prompt;
     renderSampleThumbnails();
     selectDefaultImage();
-    refreshVideoDevices().then(() => {
-      if (!state.cameraActive) populateDeviceSelect();
-    });
   } else {
     els.cameraState.textContent = "状态 -";
     els.cameraQuestion.textContent = "";
@@ -987,6 +985,8 @@ async function startCamera(deviceId) {
     state.cameraStream.getVideoTracks?.()[0]?.getSettings?.().deviceId ||
     deviceId;
   populateDeviceSelect(activeId);
+  // Reveal the camera device dropdown only while the camera is in use.
+  els.cameraDeviceRow.hidden = false;
   setCameraButtonEnabled();
 }
 
@@ -998,6 +998,7 @@ function stopCameraStream() {
   els.cameraVideo.srcObject = null;
   state.cameraActive = false;
   els.cameraStartBtn.classList.remove("is-active");
+  els.cameraDeviceRow.hidden = true;
 }
 
 function captureFromCamera() {