feat(quick-261016-nqk): ListExtendRecords and FormRecordTitle admin hooks (G-18.1-4)

pact.ListExtendRecords fills unstored fields of one list page before its
columns are read (WinterCMS listExtendRecords); such columns compile
unsortable and refuse sortable/searchable. pact.FormRecordTitle names a
record; the show, create and update responses send it as meta.title.

modules/cabana/example_extendrecords_test.go

@@ -0,0 +1,46 @@
+package cabana_test
+
+import (
+	"context"
+
+	"git.golem15.com/golem15/summercms/modules/pact"
+	"gorm.io/gorm"
+)
+
+// Ticket is a support ticket. OwnerEmail is not stored: the list's
+// owner_email column shows what ListExtendRecords puts there.
+type Ticket struct {
+	ID         uint   `gorm:"column:id;primaryKey"`
+	OwnerID    uint   `gorm:"column:owner_id"`
+	OwnerEmail string `gorm:"-:all;column:owner_email"`
+}
+
+// TicketsController is an admin controller with a computed column.
+type TicketsController struct{}
+
+var _ pact.ListExtendRecords = TicketsController{}
+
+// ListExtendRecords fills the owner e-mails of one list page with one
+// query. The framework calls it once per page, before the columns are read.
+func (TicketsController) ListExtendRecords(ctx context.Context, db *gorm.DB, records []any) error {
+	ids := make([]uint, 0, len(records))
+	for _, record := range records {
+		ids = append(ids, record.(*Ticket).OwnerID)
+	}
+	var owners []struct {
+		ID    uint
+		Email string
+	}
+	if err := db.WithContext(ctx).Table("acme_owners").Select("id, email").Where("id IN ?", ids).Scan(&owners).Error; err != nil {
+		return err
+	}
+	emails := make(map[uint]string, len(owners))
+	for _, owner := range owners {
+		emails[owner.ID] = owner.Email
+	}
+	for _, record := range records {
+		ticket := record.(*Ticket)
+		ticket.OwnerEmail = emails[ticket.OwnerID]
+	}
+	return nil
+}