chore(ops): add deployment backups restore docs and health checks

Closes the three operational blockers from the production readiness review.

deploy.sh now takes a database backup before it builds, stops or replaces
anything, and aborts the deploy if the backup fails — so no deploy proceeds
without a restore point. Dumps are gzipped and timestamped into
/opt/job-tracker/backups (override with BACKUP_DIR), so one deploy never
overwrites an earlier backup. Credentials come from the existing connection
string and travel via MYSQL_PWD, never on the command line, so they cannot reach
the process list or the deploy log. A dump that is empty or missing CREATE TABLE
is rejected, because a truncated file that looks like a restore point is worse
than none. SQLite deployments get their data volume tarred instead. Nothing is
ever deleted automatically; retention is documented as manual.

deploy/README.md documents backup creation, location, retention, database
restore, application rollback, and when to use which — restore and rollback kept
distinct, because a bad deploy usually needs only the rollback and restoring
would discard everything written since the dump.

Health checks now cover backend and frontend, which previously had none. GET
/health is anonymous, cheap, and deliberately does not touch the database: a
health check that queried MariaDB would restart a healthy backend whenever the
database blipped, and would hand out an unauthenticated way to probe database
availability. The backend image gains curl on the existing chromium apt layer,
since the aspnet runtime ships neither curl nor wget. frontend now waits for
backend to be healthy rather than merely started, because nginx proxies /api and
refuses to start when the upstream cannot be resolved.

Verified against real containers, no production data: backup from a seeded
MariaDB 11; restore into a clean MariaDB 11 with rows identical; bad credentials
and a missing connection string both abort non-zero and leave no partial file;
SQLite volume backup produces a readable archive; backend and frontend both
reach healthy; and a backend pointed at an unreachable database exits and is
reported unhealthy, so a broken deploy cannot present as a running stack.

Incidentally confirmed the earlier authorization work: with Auth:Require unset,
/health returns 200 while /api/jobapplications returns 401.

393 backend tests pass.

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

deploy/deploy.sh

@@ -28,6 +28,131 @@ compose() {
   docker compose "$@"
 }
 
+# ---------------------------------------------------------------------------
+# Database backup, taken BEFORE anything is stopped, built or replaced.
+#
+# A failed backup fails the deploy. The startup reconciler is additive and never
+# drops a table holding rows, but "additive" is a property of the code, not a
+# guarantee about the disk — and the first deploy after a schema change is
+# exactly when a restore point matters. See deploy/README.md.
+# ---------------------------------------------------------------------------
+BACKUP_DIR="${BACKUP_DIR:-/opt/job-tracker/backups}"
+
+backup_database() {
+  if [ "${DEPLOY_SKIP_DB_BACKUP:-false}" = "true" ]; then
+    echo "WARNING: DEPLOY_SKIP_DB_BACKUP=true — deploying with no restore point. Emergency use only."
+    return 0
+  fi
+
+  local provider="${DATABASE_PROVIDER:-sqlite}"
+  local stamp
+  stamp="$(date -u +%Y%m%dT%H%M%SZ)"
+  mkdir -p "$BACKUP_DIR"
+
+  if [ "$provider" != "mysql" ] && [ "$provider" != "mariadb" ]; then
+    # SQLite lives in the jobtracker_data volume. Tar it from a throwaway container
+    # so the host needs no sqlite tooling and no knowledge of the volume layout.
+    local target="$BACKUP_DIR/jobtracker-sqlite-${stamp}.tar.gz"
+    echo "Backing up SQLite data volume to ${target}"
+    # The archive path is built inside the container: passing /backup/... as an argument
+    # gets rewritten by MSYS path translation when the script is run from Git Bash.
+    if ! docker run --rm \
+        -v jobtracker_data:/data:ro \
+        -v "$BACKUP_DIR":/backup \
+        -e ARCHIVE_NAME="$(basename "$target")" \
+        alpine:3 sh -c 'tar czf "/backup/$ARCHIVE_NAME" -C /data .'; then
+      echo "SQLite volume backup FAILED. Aborting deploy."
+      return 1
+    fi
+    verify_backup "$target"
+    return $?
+  fi
+
+  local cs="${JOBTRACKER_CONNECTION_STRING:-}"
+  if [ -z "$cs" ]; then
+    echo "DATABASE_PROVIDER=${provider} but JOBTRACKER_CONNECTION_STRING is empty. Aborting deploy."
+    return 1
+  fi
+
+  # Parse the ADO.NET connection string. Keys are case-insensitive in .NET, so match that.
+  local db_host db_port db_name db_user db_pass
+  db_host="$(sed -n 's/.*[Ss]erver=\([^;]*\).*/\1/p' <<<"$cs")"
+  db_port="$(sed -n 's/.*[Pp]ort=\([^;]*\).*/\1/p' <<<"$cs")"
+  db_name="$(sed -n 's/.*[Dd]atabase=\([^;]*\).*/\1/p' <<<"$cs")"
+  db_user="$(sed -n 's/.*[Uu]ser[ ]*[Ii]*[Dd]*=\([^;]*\).*/\1/p' <<<"$cs")"
+  db_pass="$(sed -n 's/.*[Pp]assword=\([^;]*\).*/\1/p' <<<"$cs")"
+  db_port="${db_port:-3306}"
+
+  if [ -z "$db_host" ] || [ -z "$db_name" ] || [ -z "$db_user" ]; then
+    echo "Could not parse host/database/user from JOBTRACKER_CONNECTION_STRING. Aborting deploy."
+    return 1
+  fi
+
+  local target="$BACKUP_DIR/jobtracker-${db_name}-${stamp}.sql.gz"
+  echo "Backing up MariaDB database '${db_name}' on ${db_host}:${db_port} to ${target}"
+
+  # The password goes via MYSQL_PWD, never on the command line, so it cannot leak
+  # into the process list or the deploy log.
+  local dump_status=0
+  if command -v mariadb-dump >/dev/null 2>&1; then
+    MYSQL_PWD="$db_pass" mariadb-dump \
+      --host="$db_host" --port="$db_port" --user="$db_user" \
+      --single-transaction --routines --events --quick \
+      "$db_name" 2>/tmp/jobtracker-backup.err | gzip -c > "$target" || dump_status=$?
+  elif command -v mysqldump >/dev/null 2>&1; then
+    MYSQL_PWD="$db_pass" mysqldump \
+      --host="$db_host" --port="$db_port" --user="$db_user" \
+      --single-transaction --routines --events --quick \
+      "$db_name" 2>/tmp/jobtracker-backup.err | gzip -c > "$target" || dump_status=$?
+  else
+    # No client on the host: run one in a container. --network host so the same
+    # host/port from the connection string resolves identically.
+    docker run --rm --network host -e MYSQL_PWD="$db_pass" mariadb:11 \
+      mariadb-dump --host="$db_host" --port="$db_port" --user="$db_user" \
+      --single-transaction --routines --events --quick \
+      "$db_name" 2>/tmp/jobtracker-backup.err | gzip -c > "$target" || dump_status=$?
+  fi
+
+  if [ "$dump_status" -ne 0 ]; then
+    echo "Database dump FAILED (exit ${dump_status}). Aborting deploy."
+    sed -e 's/password=[^ ]*/password=***/gI' /tmp/jobtracker-backup.err >&2 || true
+    rm -f "$target"
+    return 1
+  fi
+
+  verify_backup "$target" "CREATE TABLE"
+}
+
+# A dump that exists but is empty or truncated is worse than none, because it
+# looks like a restore point. Check size, and content when we know what to expect.
+verify_backup() {
+  local target="$1"
+  local expect="${2:-}"
+
+  if [ ! -s "$target" ]; then
+    echo "Backup file ${target} is missing or empty. Aborting deploy."
+    rm -f "$target"
+    return 1
+  fi
+
+  local size
+  size="$(du -h "$target" | cut -f1)"
+
+  if [ -n "$expect" ] && ! gzip -dc "$target" | grep -q "$expect"; then
+    echo "Backup ${target} does not contain '${expect}' — it is not a usable dump. Aborting deploy."
+    rm -f "$target"
+    return 1
+  fi
+
+  echo "Backup verified: ${target} (${size})"
+  echo "Retention is manual — old backups in ${BACKUP_DIR} are never deleted automatically."
+  return 0
+}
+
+if ! backup_database; then
+  exit 1
+fi
+
 build_core_with_recovery() {
   if compose build backend frontend; then
     return 0