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/tests/test_pipeline_knowledge.py

@@ -0,0 +1,38 @@
+import unittest
+
+from models import AssistantConfig
+from services.pipecat.pipeline import _knowledge_tool_description
+
+
+class KnowledgeToolDescriptionTest(unittest.TestCase):
+    def test_includes_bound_knowledge_scope(self):
+        description = _knowledge_tool_description(
+            AssistantConfig(
+                knowledge_base_name="产品服务知识库",
+                knowledge_base_description="产品价格、售后政策和退换货条件",
+            )
+        )
+
+        self.assertIn("知识库名称：产品服务知识库", description)
+        self.assertIn("资料适用范围：产品价格、售后政策和退换货条件", description)
+        self.assertIn("与该范围无关的问题不要调用", description)
+
+    def test_falls_back_when_metadata_is_empty(self):
+        description = _knowledge_tool_description(AssistantConfig())
+
+        self.assertEqual(
+            description,
+            "在当前助手绑定的知识库中检索与问题最相关的资料片段。",
+        )
+
+    def test_compacts_and_limits_description(self):
+        description = _knowledge_tool_description(
+            AssistantConfig(knowledge_base_description=("范围\n  内容 " * 200))
+        )
+
+        self.assertNotIn("\n  ", description)
+        self.assertLess(len(description), 1000)
+
+
+if __name__ == "__main__":
+    unittest.main()