herdr web ui v0.3.9

Added

• Open the files your agents write, from any device. A file path in a chat answer
  (docs/demo.mp4, ~/out/shot.png) opens in a viewer: images, video and audio that play and
  seek at once, PDFs, and the start of a text file, each with Open in new tab and Download.
  Browse files (in the header, or the command palette on a phone) lists the pane's folder
  and any other. Files stream from disk with ranges, so a large video costs the server no memory;
  HTML and SVG open sandboxed and text as plain text, never as script on the app's origin.

Changed

• The README's screenshots and demos are sharper and framed: recorded at 2x, in a browser window
  or a phone, with a moving camera and cursor on desktop. The phone demo no longer shows only the
  top left of the screen.