MyTraL 1.56.0

This MyTraL minor release brings:

Added

• Added a Flatpak distribution (fitness.mytral.Mytral). The package runs the local
  server and opens the UI in the default browser.
  Athlete data are stored outside of the sandbox in the standard MyTraL directory.
• Added Distro Tarball GHA workflow that builds the upstream tarball in
  rel/<major.minor.patch> branches targeting main.
• Added Distro Snap GHA workflow that builds the Snap package in
  rel/<major.minor.patch> branches targeting main.
• Added Distro Windows GHA workflow that builds the Windows installer and ZIP archive
  on a Windows runner in rel/<major.minor.patch> branches targeting main.
• Added Distro Flatpak GHA workflow that builds the Flatpak bundle in
  rel/<major.minor.patch> branches targeting main.
• Added distro-win-zip Makefile target that packages the Windows desktop executable
  into a ZIP archive (distro/windows/mytral-<version>.exe.zip).

Changed

• Removed the Waitress WSGI server from the desktop edition. The desktop app serves
  a single local, so it now uses Flask's built-in threaded server - this removes
  a dependency and simplifies installation and packaging across Snap, PPA,
  and the Windows installer.
• Updated bleach from 6.3 to 6.4.
• Updated cryptography from 46.0 to 48.0.
• Updated msgpack from 1.0 to 1.2.
• Updated pytest (dev) from 8.4 to 9.0.

Documentation

• Documented Flatpak install and build.
• Documented Snap build.

Fixed

• Fixed distro-win-installer Makefile target which depended on the Linux targets.

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