Add SPIN

[from104]

SPIN — a tactic board and drill planner for powerchair football (power soccer).
Open source (MIT), no account, no telemetry.

• Repository: https://github.com/from104/spin
• Release with the AppImage: https://github.com/from104/spin/releases/tag/v0.6.9
• Web version: https://spin.atit.app

Checked against the requirements in the README before submitting:

• Built on ubuntu-22.04 in CI, so it does not require a newer glibc than the oldest supported LTS
• Runs under X11 (verified: forced GDK_BACKEND=x11, process stays alive)
• Runs without an Internet connection (verified with outbound traffic blackholed) — it is a
  local-first app; sign-in and share links are optional
• Desktop file passes desktop-file-validate
• Ships an AppStream metainfo file in usr/share/metainfo/, and it passes
  appstreamcli validate --no-net
• Icons at 32/128/256 in usr/share/icons/hicolor, .DirIcon is the 256×256 one
• Filename follows the standard nomenclature: SPIN-0.6.9-x86_64.AppImage

No screenshots are declared in the metainfo yet — the main window is the app itself (a court with
the tactic board), not a dialog, so the automatic screenshot should be representative.