Move Borg repo to local backups and remove JuiceFS

Use /mnt/borg-backups in place of /mnt/object_storage for Borg.

Remove JuiceFS and Redis artifacts (tasks, templates, service configs)
and delete borg-local-sync tooling. Update borg-backup service
ReadWritePaths, remove Plex slow tvshows mount, add system sysctl
performance tunings, and apply minor code and flake.lock updates.

ansible/tasks/servers/services/plex/docker-compose.yml.j2

@@ -16,7 +16,6 @@ services:
       - {{ plex_data_dir }}/transcode:/transcode
       - /mnt/data/movies:/movies
       - /mnt/data/tvshows:/tvshows
-      - /mnt/object_storage/tvshows:/tvshows_slow
       - /mnt/data/music:/music
     deploy:
       resources: