Summary

• Syncs the volume slider with the actual YouTube iframe player using postMessage, including mute/unmute handling and reapplying volume on iframe load and ready events.
• Improves the player drawer UX with clearer playlist controls, active-item indicators, tooltips, and a cleaner empty state prompt.
• Adds inline validation and keyboard handling to the custom URL editor, including autofocus, Escape-to-cancel, and explicit error messages.
• Adjusts the iframe sandbox and removes modestbranding from the embed URL builder.

Testing

• Not run (not requested).
• Expected checks: bun fmt.
• Expected checks: bun lint.
• Expected checks: bun typecheck.