MKV Muxing Batch GUI 2.8.1

Added

• Add a persistent main-window status toolbar showing the detected MKVToolNix
  version, missing-tool details, download progress, dependency updates, and a
  manual application/dependency update check.
• Add a user-local MKVToolNix installer that resolves the publisher's latest
  stable version, verifies its platform metadata, validates both downloaded
  command-line tools, and activates them without administrator privileges.

Fixed

• Make the missing-dependency prompt start a visible in-app download instead of
  silently delegating to a browser that may not open.
• Extract the Linux AppImage once and run its real command-line tools with the
  included libraries, avoiding FUSE requirements and polluted version output.