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_test.go

@@ -3,6 +3,7 @@ package user
 import (
 	"bytes"
 	"context"
+	"encoding/base64"
 	"strings"
 	"testing"
 
@@ -77,6 +78,40 @@ func TestConsoleWithDBOpensFromConfigWhenUnpublished(t *testing.T) {
 	}
 }
 
+// TestBackfillHandlesOpensFromConfigWhenUnpublished runs user:backfill-handles
+// as the console does: no published database, only database.dsn in the config.
+func TestBackfillHandlesOpensFromConfigWhenUnpublished(t *testing.T) {
+	_, gdb := sessionApp(t, "0s")
+	user := insertUser(t, gdb, "backfill-unpublished@example.test", "correct-horse")
+	if err := gdb.Model(user).Update("handle", nil).Error; err != nil {
+		t.Fatal(err)
+	}
+	app := backpack.New(sessionConfig(t))
+	if err := app.Config.Set("database.dsn", sessionDSN); err != nil {
+		t.Fatal(err)
+	}
+	// Opening a database also loads the encryption keys from app.key.
+	if err := app.Config.Set("app.key", base64.StdEncoding.EncodeToString([]byte("0123456789abcdef0123456789abcdef"))); err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := app.Lookup[*gorm.DB](); ok {
+		t.Fatal("setup: a database is published")
+	}
+	cmd := commandNamed(t, (&Plugin{app: app}).Commands(), "user:backfill-handles")
+	var buf bytes.Buffer
+	out := bonfire.NewOutput(nil, &buf, &buf)
+	if err := cmd.Run(context.Background(), emailArg{}, out); err != nil {
+		t.Fatalf("run: %v (output %q)", err, buf.String())
+	}
+	var fresh models.User
+	if err := gdb.First(&fresh, user.ID).Error; err != nil {
+		t.Fatal(err)
+	}
+	if fresh.Handle == nil || *fresh.Handle == "" {
+		t.Fatal("the user still has no handle")
+	}
+}
+
 func commandNamed(t *testing.T, cmds []bonfire.Command, name string) bonfire.Command {
 	t.Helper()
 	for _, candidate := range cmds {