Implemented keyboard shortcuts for play/pause (spacebar) and seeking backward/forward (arrow keys) in the video editor. Shortcuts are disabled when typing in input fields to prevent interference.
Introduces a new optional 'posterUrl' property to the MEDIA_DATA object on the window, updating both the runtime initialization and TypeScript type declaration.
Introduces an audio-poster.jpg image and updates both chapters and video editor React video player components to display a poster image for audio files when no poster is provided. Also adds a posterUrl field to MEDIA_DATA and ensures fallback logic for poster images is consistent across iOS and standard video players.
