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.

compose.yml

@@ -57,7 +57,7 @@ services:
       interval: 30s
       timeout: 10s
       retries: 10
-      start_period: 1m
+      start_period: 15m
  
   db:
     image: mysql:8.0
@@ -72,9 +72,9 @@ services:
     deploy:
       labels:
         - "backupbot.backup=true"
-        - "backupbot.backup.pre-hook=mysqldump -u root -p\"$$(cat /run/secrets/db_password)\" ghost --tab /var/lib/mysql-files/"
+        - 'backupbot.backup.pre-hook=mysqldump -u root -p"$$(cat /run/secrets/db_password)" --single-transaction --routines --triggers --databases ghost | gzip > /var/lib/mysql/backup.sql.gz'
-        - "backupbot.backup.post-hook=rm -rf /var/lib/mysql-files/*"
+        - "backupbot.backup.volumes.mysql.path=backup.sql.gz"
-        - "backupbot.backup.path=/var/lib/mysql-files/"
+        - 'backupbot.restore.post-hook=gunzip -c /var/lib/mysql/backup.sql.gz | mysql -u root -p"$$(cat /run/secrets/db_password)"'
 
     healthcheck:
       test: ["CMD", "mysqladmin", "ping", "-h", "localhost", "-u", "root", "-p\"$$(cat /run/secrets/db_password)\""]