refactor: remove serde from domain entities for Clean Architecture compliance

- Remove Serialize/Deserialize from File, Folder, Session, User, Contact entities
- Create contact_persistence_dto.rs for JSONB persistence in infrastructure layer
- Update contact_pg_repository to use persistence DTOs
- Fix dependency on zip crate (downgrade from 7.2.0 to 2.1.0)
- Fix unused variable warnings in main.rs
- Move PathService import from domain to infrastructure
- Add missing fields to CoreServices and RepositoryServices
- Create proper service initialization in main.rs

Clean Architecture improvements:
- Domain layer no longer depends on serde framework
- Persistence concerns isolated to infrastructure layer
- TokenClaims in auth_service.rs is only exception (required for JWT)

src/application/services/file_retrieval_service.rs

@@ -18,13 +18,6 @@ impl FileRetrievalService {
     pub fn new(file_repository: Arc<dyn FileReadPort>) -> Self {
         Self { file_repository }
     }
-    
-    /// Crea un stub para pruebas
-    pub fn default_stub() -> Self {
-        Self {
-            file_repository: Arc::new(crate::infrastructure::repositories::FileFsReadRepository::default_stub())
-        }
-    }
 }
 
 #[async_trait]