Fix foreign key constraint: delete mail_objects before mails

Added deletion of mail_objects before deleting mail_messages to
avoid foreign key constraint violation. The mail_objects table
has a foreign key to mail_messages.

Complete deletion order:
1. Clean up auxiliary tables
2. Unlink mails from jobs
3. Delete mail_objects
4. Delete jobs (cascades to runs)
5. Delete mails

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

containers/backupchecks/src/backend/app/main/routes_settings.py

@@ -252,6 +252,17 @@ def settings_jobs_delete_orphaned():
                 {"job_ids": job_ids},
             )
 
+        # Delete mail_objects before deleting mails
+        # mail_objects.mail_message_id references mail_messages.id
+        if mail_message_ids:
+            from sqlalchemy import text, bindparam
+            _safe_execute(
+                text("DELETE FROM mail_objects WHERE mail_message_id IN :mail_ids").bindparams(
+                    bindparam("mail_ids", expanding=True)
+                ),
+                {"mail_ids": mail_message_ids},
+            )
+
         # Delete all orphaned jobs (runs/objects are cascaded via ORM relationships)
         for job in orphaned_jobs:
             db.session.delete(job)