feat: daily encrypted database backup to a bucket of its own

A backup service runs pg_dump every day at 03:00 Brasília, checks the archive,
encrypts it with age to a public key and uploads it with a token for that
bucket only. The server cannot read or delete backups: the private key stays
with the owner, the bucket's lifecycle rule expires copies and its lock stops
early deletion. Each run is recorded and shown on the Kanban's Integrations
tab. tests/backup_test.py backs up, restores into a scratch database and
compares the rows in CI. Setup and restore: docs/BACKUP.md.

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

deploy/Dockerfile.api

@@ -13,8 +13,11 @@ LABEL org.opencontainers.image.title="DTF Portal/API" \
 # The base is pinned, so its OS packages are frozen at the digest's build date.
 # Upgrade them here or the image ships known-fixed Debian vulnerabilities, which
 # is what the production image was doing while the local one already did this.
+# pg_dump and age are for the database backup (ops/db_backup.py). Debian 13
+# ships PostgreSQL 17, the server's major version, which pg_dump must match.
 RUN apt-get update \
     && apt-get upgrade -y \
+    && apt-get install -y --no-install-recommends postgresql-client-17 age \
     && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app

deploy/portainer.env.example

@@ -51,6 +51,13 @@ MAX_PENDING_UPLOADS=10
 MAX_UPLOAD_BYTES=5368709120
 UPLOAD_PART_BYTES=8388608
 SCAN_MAX_BYTES=134217728
+# Daily encrypted database backup to its own bucket (docs/BACKUP.md).
+BACKUP_S3_ENDPOINT=https://<account>.r2.cloudflarestorage.com
+BACKUP_BUCKET=dtf-backups
+BACKUP_ACCESS_KEY_ID=TBD
+BACKUP_SECRET_ACCESS_KEY=TBD
+BACKUP_AGE_RECIPIENT=age1...
+BACKUP_HOUR=3
 
 # Names of external Portainer/Docker Swarm secrets, never their values.
 DATABASE_URL_SECRET=TBD