Feature/memory work (#61)

* refactor(conversation): separate service and repository layers for conversation module

- Split ConversationService and repository/UnitOfWork layers
- Service layer now only handles business logic and orchestration
- Repository layer handles all direct database operations
- UnitOfWork encapsulates transactional operations for messages
- Ensured all public methods have clear English docstrings with arguments, return values, and exceptions

* feat(memory): implement work memory endpoints and services

- Added API routes for conversation count, conversation list, messages, and detail.
- Integrated ConversationService for database queries and LLM-based summary generation.

* feat(memory): implement work memory endpoints and services

- Added API routes for conversation count, conversation list, messages, and detail.
- Integrated ConversationService for database queries and LLM-based summary generation.

* feat(workflow): fix issues causing workflow failures

if-else None value error
knowledge empty list rerank
end node output none node value
assigner input none value

* feat(memory): convert memory file creation time to timestamp and include title and first-line fields in file type

* fix(memory): fix serialization output and default value issues

* fix(workflow): fix issue with hybrid search logic in knowledge retrieval node

api/app/services/memory_perceptual_service.py

@@ -99,7 +99,7 @@ class MemoryPerceptualService:
                 "keywords": content.keywords,
                 "topic": content.topic,
                 "domain": content.domain,
-                "created_time": memory.created_time.isoformat() if memory.created_time else None,
+                "created_time": int(memory.created_time.timestamp()*1000),
                 **detail
             }
 
@@ -141,8 +141,9 @@ class MemoryPerceptualService:
                     perceptual_type=PerceptualType(memory.perceptual_type),
                     file_path=memory.file_path,
                     file_name=memory.file_name,
+                    file_ext=memory.file_ext,
                     summary=memory.summary,
-                    created_time=memory.created_time,
+                    created_time=int(memory.created_time.timestamp()*1000),
                     storage_type=FileStorageType(memory.storage_service),
                 )
                 memory_items.append(memory_item)