v0.6.0

Added

• Rich preview: video + audio. The preview pane now plays video (.mp4, .webm)
  and audio (.mp3, .wav, .ogg, .m4a, .flac) inline via native HTML5 players,
  with the matching grid icons (🎬 / 🎵). Video previews also show the embedded-metadata
  card (prompt fields + Load on canvas + Copy JSON). The allowed extensions are
  configurable via files.video_extensions / files.audio_extensions in config.json.
• Media is served via a Range-aware response (206 Partial Content), so seeking works
  and Safari plays correctly. The /preview stored-XSS defenses are unchanged: only the
  image/video/audio allow-lists preview inline, always with X-Content-Type-Options: nosniff;
  HTML/SVG/other active types are still refused.