feat(agent): 实现 Agent Runtime LLM 配置与消息元数据结构化支持

backend/src/core/config/static/database/system_agents.yaml

@@ -4,15 +4,18 @@ agents:
     status: active
     config:
       temperature: 0.7
+      max_tokens: null
     
   - agent_type: TASK_EXECUTION
     llm_model_code: deepseek-v3.2
     status: active
     config:
       temperature: 0.7
+      max_tokens: null
     
   - agent_type: RESULT_REPORTING
     llm_model_code: deepseek-v3.2
     status: active
     config:
       temperature: 0.7
+      max_tokens: null