Fix backups for JSON-file storage + healthcheck; drop handoff folder

- backup.sh: snapshot all of /data as timestamped tar.gz to local NAS path;
  push to B2 only when a real bucket/key is set (no more nonexistent app.db).
- compose: working CMD-SHELL healthcheck; mount /mnt/user/Backup target.
- remove the accidentally committed moon-household-budget-handoff/ scaffolding.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.yml

@@ -1,6 +1,6 @@
 # Moon Household Budget — self-contained stack.
-#   app    : the Python web app (SQLite on the ./data volume — no DB container)
-#   backup : rclone sidecar that snapshots ./data to Backblaze B2 on a loop
+#   app    : the Python web app (JSON-file storage on the ./data volume)
+#   backup : sidecar that tar.gz-snapshots ./data locally + optionally to B2
 #
 # Deployed on the Unraid NAS under /mnt/user/appdata/moon-household-budget/.
 # Bring up with:  docker compose up -d --build
@@ -15,9 +15,9 @@ services:
       - "8052:8000"          # http://192.168.0.5:8052
     env_file: .env
     volumes:
-      - ./data:/data         # SQLite db + uploaded images live here
+      - ./data:/data         # budget JSON files + uploaded images live here
     healthcheck:
-      test: ["CMD", "curl", "-fsS", "http://localhost:8000/", "||", "exit", "1"]
+      test: ["CMD-SHELL", "curl -fsS http://localhost:8000/ || exit 1"]
       interval: 30s
       timeout: 5s
       retries: 3
@@ -29,4 +29,5 @@ services:
     restart: unless-stopped
     env_file: .env
     volumes:
-      - ./data:/data:ro      # read-only — backup never writes app data
+      - ./data:/data:ro                              # read-only — never writes app data
+      - /mnt/user/Backup/moon-household-budget:/backups   # local snapshot target