Add knowledge retrieval configuration to Assistant model and related components

- Introduce new fields for knowledge retrieval configuration in AssistantConfig and Assistant models, including mode, top_n, and score_threshold.
- Implement KnowledgeRetrievalConfig schema with validation for top_n.
- Update backend services and routes to handle knowledge retrieval settings.
- Enhance frontend components to support knowledge retrieval configuration, including a new dialog for advanced settings.
- Add tests for knowledge retrieval configuration validation and description generation.

backend/models.py

@@ -76,6 +76,15 @@ class AssistantConfig(BaseModel):
     # Prompt assistant reusable tools. Execution remains type-specific in the pipeline.
     tools: list[RuntimeTool] = Field(default_factory=list)
     knowledge_base_id: str | None = None
+    knowledge_base_name: str = ""
+    knowledge_base_description: str = ""
+    knowledge_retrieval_config: dict = Field(
+        default_factory=lambda: {
+            "mode": "automatic",
+            "top_n": 5,
+            "score_threshold": 0.0,
+        }
+    )
 
     # workflow 类型:节点图(nodes/edges)。非 workflow 为空,引擎据此决定是否启用。
     graph: dict = {}