2configs.services.flix.ipfs: allow ipfs-upload to write into games/
Adjusts /var/download/games to ipfs:users mode 2775 so the upload
service (running as ipfs) can write into it while lass keeps write via
the users group. systemd-tmpfiles refuses to bootstrap this transition
when child and parent have different owners, so the first chown was
done out-of-band; this `z` rule keeps the perms from drifting.
Also drops the non-existent `download` group from the staging dir
tmpfiles entries (download group only exists on the yellow container,
not on the host).
Assisted-by: Claude Code (claude-opus-4-7)