Harden backup integrity, implement verified restore and safe upgrades

tests/Dockerfile

@@ -0,0 +1,4 @@
+FROM debian:trixie-slim
+RUN apt-get update && apt-get install -y --no-install-recommends bash python3 rsync zstd gzip tar rclone shellcheck sudo mariadb-server mariadb-client ca-certificates && rm -rf /var/lib/apt/lists/*
+WORKDIR /src
+CMD ["bash", "tests/run.sh"]