feat(32-03): create JKVideoButton with colocated loading state

- Extracted video button from JKSessionScreen
- Local loading state prevents parent re-renders
- memo() wrapper for render optimization
- Preserves 10-second loading timeout behavior
- Handles permission checks via canVideo prop

jam-ui/src/components/client/JKVideoButton.js

@@ -0,0 +1,78 @@
+import React, { useState, useCallback, memo } from 'react';
+import { Button, Spinner } from 'reactstrap';
+import { toast } from 'react-toastify';
+import PropTypes from 'prop-types';
+import videoIcon from '../../assets/images/icons8-video-call-50.png';
+
+/**
+ * Self-contained video button with colocated loading state.
+ * Loading state changes only re-render this component, not the parent.
+ *
+ * State colocation: https://kentcdodds.com/blog/state-colocation-will-make-your-react-app-faster
+ */
+const JKVideoButton = memo(({
+  canVideo,
+  getVideoUrl,
+  onUpgradePrompt,
+  className
+}) => {
+  const [loading, setLoading] = useState(false);
+
+  // Open external link in new window/tab
+  const openExternalLink = useCallback((url) => {
+    window.open(url, '_blank', 'noopener,noreferrer');
+  }, []);
+
+  const handleClick = useCallback(async () => {
+    if (!canVideo()) {
+      onUpgradePrompt();
+      return;
+    }
+
+    try {
+      setLoading(true);
+
+      // Get video conferencing room URL from server
+      const response = await getVideoUrl();
+      const videoUrl = `${response.url}&audiooff=true`;
+
+      // Open video URL in new browser window/tab
+      openExternalLink(videoUrl);
+
+    } catch (error) {
+      toast.error('Failed to start video session');
+    } finally {
+      // Keep loading state for 10 seconds to prevent multiple clicks
+      setTimeout(() => setLoading(false), 10000);
+    }
+  }, [canVideo, getVideoUrl, onUpgradePrompt, openExternalLink]);
+
+  return (
+    <Button
+      className={className || 'btn-custom-outline'}
+      outline
+      size="md"
+      onClick={handleClick}
+      disabled={loading}
+    >
+      <img
+        src={videoIcon}
+        alt="Video"
+        style={{ width: '20px', height: '20px', marginRight: '0.3rem' }}
+      />
+      {loading && <Spinner size="sm" />}
+      &nbsp;Video
+    </Button>
+  );
+});
+
+JKVideoButton.displayName = 'JKVideoButton';
+
+JKVideoButton.propTypes = {
+  canVideo: PropTypes.func.isRequired,
+  getVideoUrl: PropTypes.func.isRequired,
+  onUpgradePrompt: PropTypes.func.isRequired,
+  className: PropTypes.string
+};
+
+export default JKVideoButton;