feat: add model_config parameter support for Dify assistant type apps (#1796)

* Initial plan

* feat: add model_config parameter support for Dify assistant type

- Add model_config parameter to AsyncDifyServiceClient.chat_messages method
- Add _get_model_config helper method to DifyServiceAPIRunner
- Pass model_config from pipeline configuration to all chat_messages calls
- Add model-config configuration field to dify-service-api schema in ai.yaml
- Support optional model configuration for assistant type apps in open-source Dify

Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

* refactor: improve model_config implementation based on code review

- Simplify _get_model_config method logic
- Add more descriptive comment about model_config usage
- Clarify when model_config is used (assistant type apps)

Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

* feat: only modify client.py

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>
Co-authored-by: Junyan Qin <rockchinq@gmail.com>

src/langbot/libs/dify_service_api/v1/client.py

@@ -32,6 +32,7 @@ class AsyncDifyServiceClient:
         conversation_id: str = '',
         files: list[dict[str, typing.Any]] = [],
         timeout: float = 30.0,
+        model_config: dict[str, typing.Any] | None = None,
     ) -> typing.AsyncGenerator[dict[str, typing.Any], None]:
         """发送消息"""
         if response_mode != 'streaming':
@@ -42,6 +43,16 @@ class AsyncDifyServiceClient:
             trust_env=True,
             timeout=timeout,
         ) as client:
+            payload = {
+                'inputs': inputs,
+                'query': query,
+                'user': user,
+                'response_mode': response_mode,
+                'conversation_id': conversation_id,
+                'files': files,
+                'model_config': model_config or {},
+            }
+
             async with client.stream(
                 'POST',
                 '/chat-messages',
@@ -49,14 +60,7 @@ class AsyncDifyServiceClient:
                     'Authorization': f'Bearer {self.api_key}',
                     'Content-Type': 'application/json',
                 },
-                json={
-                    'inputs': inputs,
-                    'query': query,
-                    'user': user,
-                    'response_mode': response_mode,
-                    'conversation_id': conversation_id,
-                    'files': files,
-                },
+                json=payload,
             ) as r:
                 async for chunk in r.aiter_lines():
                     if r.status_code != 200: