fix: user:backfill-handles opens its own database

- without a published *gorm.DB the command opens one with lagoon.OpenFromApp
  for its run and closes it, as the plugin's other commands do (withDB)
- TestBackfillHandlesOpensFromConfigWhenUnpublished; README CLI note

console/backfill_handles.go

@@ -8,10 +8,14 @@ import (
 	"git.golem15.com/golem15/sm-user-plugin/models"
 	"git.golem15.com/golem15/summercms/modules/backpack"
 	"git.golem15.com/golem15/summercms/modules/bonfire"
+	"git.golem15.com/golem15/summercms/modules/lagoon"
 	"gorm.io/gorm"
 )
 
 // BackfillHandles fills a unique handle on every user row that still has none.
+// It uses the database the serve command published or, when it runs as a
+// console command, opens one from the config for the duration of the run,
+// as the plugin's other commands do.
 func BackfillHandles(app *backpack.App) bonfire.Command {
 	return bonfire.Command{
 		Name:        "user:backfill-handles",
@@ -22,7 +26,12 @@ func BackfillHandles(app *backpack.App) bonfire.Command {
 			}
 			gdb, ok := app.Lookup[*gorm.DB]()
 			if !ok || gdb == nil {
-				return fmt.Errorf("user:backfill-handles: database is not configured")
+				sqlDB, opened, err := lagoon.OpenFromApp(ctx, app)
+				if err != nil {
+					return fmt.Errorf("user:backfill-handles: %w", err)
+				}
+				defer sqlDB.Close()
+				gdb = opened
 			}
 			var users []models.User
 			if err := gdb.WithContext(ctx).Where("handle IS NULL OR handle = ''").Find(&users).Error; err != nil {