fix(backup) + chore: upgrade to 1.3.0+6.42.0-alpine

- Inline mysqldump/gunzip into backupbot.backup.pre-hook and
  backupbot.restore.post-hook label values on the db service.
  Single-file gzipped dump (--single-transaction --routines
  --triggers --databases ghost) is written into the mysql volume
  at /var/lib/mysql/backup.sql.gz; the volume is what backupbot
  snapshots, so the dump survives the round-trip and the restore
  hook re-imports it. Replaces the previous mysqldump --tab
  backup that shipped with no restore hook (silent data loss on
  restore, since the mysql data volume itself wasn't backed up).
- Drop mysql_backup.sh, its config mount, and MYSQL_BACKUP_VERSION
  in favour of the inline label pattern used by
  akaunting / engelsystem / forgejo.
- Raise app healthcheck start_period 1m -> 15m to accommodate
  slow fresh-DB migration on first boot.
- Upgrade ghost image to 6.42.0-alpine; bump recipe version to
  1.3.0+6.42.0-alpine.

abra.sh

@@ -1 +1 @@
-export GHOST_ENTRYPOINT_VERSION=v1
+export GHOST_ENTRYPOINT_VERSION=v1