fix: update sexy_db credentials to sexy:sexy

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

_backup/backup.sh

@@ -36,7 +36,7 @@ declare -A DATABASES=(
   [blinko_db]="blinko:blinko"
   [gitea_db]="gitea:gitea"
   [mattermost_db]="mattermost:mattermost"
-  [sexy_db]="directus:directus"
+  [sexy_db]="sexy:sexy"
   [immich_db]="immich:immich"
   [coolify_db]="coolify:coolify"
 )