Add interface design references and principles; implement sport service tests

- Introduced critique, example, principles, and validation documents for interface design.
- Enhanced backend service with coverage threshold and fixed variable declaration in sport service.
- Added comprehensive tests for create, update, and list sports functionalities.

apps/backend/src/modules/sport/services/sport.service.ts

@@ -71,7 +71,7 @@ export async function createSport(input: CreateSportInput) {
     return err(Errors.conflict('Ya existe un deporte con ese nombre.'));
   }
 
-  var created = db.sport.create({
+  const created = await db.sport.create({
     data: {
       id: uuidv7(),
       name: input.name.trim(),