feat(catalog): class template editing

Templates were delete-and-recreate only. Adds PUT
/v1/catalog/class-templates/{id} across repository, service (sharing
the create-time validation), route, spec, and client; the classes tab
gets a pencil action that loads the row into the form with a
save/cancel affordance.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/internal/db/classes.go

@@ -71,6 +71,24 @@ func (r *PGRepository) CreateClassTemplate(ctx context.Context, params CreateCla
 	return record, err
 }
 
+func (r *PGRepository) UpdateClassTemplate(ctx context.Context, templateID string, params CreateClassTemplateParams) (ClassTemplateRecord, error) {
+	var record ClassTemplateRecord
+	err := r.pool.QueryRow(ctx, `
+		UPDATE class_templates
+		SET title = $2, duration_minutes = $3, capacity = $4
+		WHERE id = $1
+		RETURNING `+classTemplateColumns+`
+	`, templateID, params.Title, params.DurationMinutes, params.Capacity).Scan(
+		&record.ID,
+		&record.TenantID,
+		&record.Title,
+		&record.DurationMinutes,
+		&record.Capacity,
+		&record.CreatedAt,
+	)
+	return record, err
+}
+
 func (r *PGRepository) DeleteClassTemplate(ctx context.Context, templateID string) error {
 	_, err := r.pool.Exec(ctx, `DELETE FROM class_templates WHERE id = $1`, templateID)
 	return err