M2c-dev: development compose stack, backup job, Firebase setup docs

infra/dev: compose stack on the Mac (server kvitt-server:dev, on-demand backup),
.env.example, build/up/logs/backup/copy-google-services scripts. No Caddy, no TLS
(debug builds accept http to private LAN addresses, AC-2.8). Bind-mounted data.
infra/backup: alpine 3.24.2 image and backup.sh (SPEC 10.9; Drive upload skipped
when RCLONE_FOLDER_ID is empty). infra/README.md for the dev stack and Firebase.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

infra/backup/Dockerfile

@@ -0,0 +1,20 @@
+# Kvitt backup job image (SPEC §10.3, §10.9): alpine with sqlite, gzip, tar, rclone and backup.sh run by crond.
+# Versions resolved 2026-10-17: alpine 3.24.2 (Docker Hub official image, multi-arch index digest below);
+# packages from Alpine v3.24 main/community: sqlite 3.53.4, rclone 1.74.1, tar 1.35, tzdata 2026e.
+FROM docker.io/library/alpine:3.24.2@sha256:294b683cb724975bec92580e1e685676bd4b50bda910ddb8c51d4cabeaec77e6
+
+RUN apk add --no-cache \
+      "sqlite~3.53" \
+      "rclone~1.74" \
+      "tar~1.35" \
+      gzip \
+      tzdata
+
+COPY backup.sh /backup.sh
+RUN chmod 0755 /backup.sh \
+ && echo '30 3 * * * /backup.sh' > /etc/crontabs/root
+
+ENV TZ=Europe/Stockholm
+# Daily at 03:30 Europe/Stockholm. The development stack runs it on demand instead
+# (`docker compose run --rm backup /backup.sh`, see infra/README.md).
+CMD ["crond", "-f", "-l", "8"]