Add Kopia backup stack with Backblaze B2 offsite target.

Protects /config, selective labdata, and nightly DB dumps; documents homelab improvement plan briefs.

stacks/roms/docker-compose.yml

@@ -11,7 +11,7 @@
 # UI env vars for ${VAR} substitution. See memory portainer-env-interpolation.
 #
 # Tiered binds: DB + RomM config + bundled-redis -> /config/romm (SSD);
-# RomM blobs (downloaded art + user saves/states) -> /storage1/labdata/romm (ZFS).
+# RomM labdata (ZFS): assets = saves/states; resources = fetched cover art (IGDB etc.).
 # The labdata/romm/* targets are auto-created by Docker as root on first start.
 #
 # Only romm joins `edge` (Caddy proxies romm:8080); romm-db stays on `roms` only.