Audio/video preview viewer for dsh-better-sidebar

Key features

• HTTP Range (206) seeking — the browser can jump anywhere in a long video
• Streamed responses (fs.createReadStream) — no whole-file buffering
• Whole-filesystem scope behind the same browser trust fence the built-in /api documents (loopback Host + same-origin markers), matching the official directory-picker browse backend — the sidebar explorer browses outside the session cwd (e.g.
• a music folder in /Documents), and media files must play wherever the explorer can open them