Add Kopia backup stack with Backblaze B2 offsite target.

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

stacks/backup/SCOPE.md

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+# What we back up (and skip)
+
+**Rule:** everything irreplaceable or slow to rebuild — **not** ROM files, **not** provider cover art.
+
+## Always
+
+| Path | Why |
+|------|-----|
+| `/config` | App state, DBs, CouchDB vault — **includes RomM MariaDB** (`/config/romm/mariadb`) |
+| `/config/backup/dumps` | Nightly SQL dumps — **includes `romm-db`** |
+
+## RomM
+
+Per [RomM docs](https://docs.romm.app/): **`assets` = saves/states**; **`resources` = fetched covers**.
+
+| Included | Path | What |
+|----------|------|------|
+| Database | `/config/romm/mariadb` + nightly dump | Scans, hashes, matches (weeks of work) |
+| Saves & states | `labdata/romm/assets` | RomM-managed save files |
+| Config/cache | `/config/romm/config`, `/config/romm/redis` | Via `/config` snapshot |
+
+| Skipped | Path | What |
+|---------|------|------|
+| Cover art | `labdata/romm/resources` | IGDB/SteamGridDB — minutes to re-fetch |
+
+## Emulation (`/storage1/Emulation`) — excluded
+
+Legacy pre-RomM tree (EmuDeck, ES-DE, 13T `roms/`, symlinks). **Not backed up offsite.** RomM is the source of truth for saves via `labdata/romm/assets` + DB.
+
+## labdata — included
+
+| Path | Why |
+|------|-----|
+| `gitea/repositories`, `gitea/lfs` | Git + LFS |
+| `famapp/minio`, `resume/minio`, `plane/minio` | User uploads |
+| `romhacks/metadata`, `romhacks/library` | Catalog work + guides/spreadsheets |
+| `romm/assets` | Saves (see RomM above) |
+
+## labdata — skipped
+
+| Path | Why |
+|------|-----|
+| `romm/resources` | Provider cover art |
+| `registry` | Re-pull images |
+| `romhacks/incoming` | Transient download queue |
+
+## Change scope
+
+Edit `snapshot-paths.txt`, bind mounts in `docker-compose.yml`, and `SCOPE.md`.