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/schemas/memory_perceptual_schema.py

@@ -39,10 +39,11 @@ class PerceptualMemoryItem(BaseModel):
     id: uuid.UUID = Field(..., description="Unique memory ID")
     perceptual_type: PerceptualType = Field(..., description="Type of perception, e.g., text, audio, or video")
     file_path: str = Field(..., description="File path in the storage service")
+    file_ext: str = Field(..., description="File extension")
     file_name: str = Field(..., description="File name")
-    summary: Optional[str] = Field(None, description="摘要")
+    summary: Optional[str] = Field(None, description="summary")
     storage_type: FileStorageType = Field(..., description="Storage type for file")
-    created_time: Optional[datetime] = Field(None, description="创建时间")
+    created_time: int = Field(..., description="create time")
 
     class Config:
         from_attributes = True
@@ -114,6 +115,8 @@ class AudioModal(BaseModel):
 
 class TextModal(BaseModel):
     section_count: int
+    title: str
+    first_line: str
 
 
 class Asset(BaseModel):