refactor: make stream smoothing parameters configurable and add models cache invalidation

- Move stream smoothing parameters (chunk_size, delay_ms) to database config
- Remove hardcoded stream smoothing constants from StreamProcessor
- Simplify dynamic delay calculation by using config values directly
- Add invalidate_models_list_cache() function to clear /v1/models endpoint cache
- Call cache invalidation on model create, update, delete, and bulk operations
- Update admin UI to allow runtime configuration of smoothing parameters
- Improve model listing freshness when models are modified

src/services/system/config.py

@@ -83,6 +83,14 @@ class SystemConfigService:
             "value": False,
             "description": "是否启用流式平滑输出，自动根据文本长度调整输出速度",
         },
+        "stream_smoothing_chunk_size": {
+            "value": 20,
+            "description": "流式平滑输出每个小块的字符数",
+        },
+        "stream_smoothing_delay_ms": {
+            "value": 8,
+            "description": "流式平滑输出每个小块之间的延迟毫秒数",
+        },
     }
 
     @classmethod