feat: 完成极简 LangGraph 架构迁移，添加 Baosi API 支持

主要变更：
- 迁移到极简 LangGraph 标准架构（START → init_state → 记忆 → Agent ⇄ Tools → finalize → END）
- 添加 Baosi API 支持，配置 ops4.7 模型
- 保留本地模型作为默认首选，Baosi 作为备选
- 新架构使用 LangGraph 原生 ToolNode 和 bind_tools
- 移除旧的混合路由、JSON 解析等复杂逻辑
- 把旧代码移到 deprecated/ 目录
- 添加新的 Agent 节点和 Tools 模块
- 添加测试脚本验证新架构
- 所有测试通过 ✓

backend/app/deprecated/reasoning.py

@@ -0,0 +1,120 @@
+"""
+React 推理节点
+使用 intent.py 进行意图推理
+"""
+
+from typing import Optional
+from datetime import datetime
+from langchain_core.runnables.config import RunnableConfig
+
+from backend.app.core.intent import react_reason_async, ReasoningResult, ReasoningAction
+from ..state import MainGraphState
+from backend.app.logger import info
+from ._utils import dispatch_custom_event, make_react_event
+
+
+async def react_reason_node(state: MainGraphState, config: Optional[RunnableConfig] = None) -> MainGraphState:
+    """React 模式推理节点：判断下一步做什么"""
+    state.current_phase = "react_reasoning"
+    state.reasoning_step += 1
+
+    info(f"[推理] 第 {state.reasoning_step} 次推理开始")
+
+    # ==================================================
+    # 优化：如果是第一次推理，检查 hybrid_router 的结果！
+    # 避免重复推理！
+    # ==================================================
+    if state.reasoning_step == 1 and state.hybrid_router.decision and state.hybrid_router.decision.reasoning_result:
+        # 有保存的推理结果，直接复用！
+        decision = state.hybrid_router.decision
+        result: ReasoningResult = decision.reasoning_result
+
+        info(f"[推理] 第1次推理，复用 hybrid_router 结果: action={result.action.name}, confidence={result.confidence}")
+        if result.reasoning:
+            info(f"[推理] 推理过程: {result.reasoning}")
+
+        # 记录推理历史
+        state.reasoning_history.append({
+            "step": state.reasoning_step,
+            "action": result.action.name,
+            "confidence": result.confidence,
+            "reasoning": result.reasoning,
+            "timestamp": datetime.now().isoformat()
+        })
+
+        # 更新状态
+        state.react_reasoning.last_reasoning = {
+            "action": result.action.name,
+            "confidence": result.confidence,
+            "reasoning": result.reasoning
+        }
+        state.react_reasoning.reasoning_result = result
+        state.last_action = result.action.name
+
+        # 发送推理事件
+        await dispatch_custom_event(
+            "react_reasoning",
+            make_react_event(
+                state.reasoning_step,
+                result.action.name,
+                result.confidence,
+                result.reasoning
+            ),
+            config
+        )
+
+        return state
+
+    # ==================================================
+    # 原来的逻辑（第二次推理或没有保存结果时使用）
+    # ==================================================
+
+    # 步骤1: 准备上下文
+    context = {
+        "retrieved_docs": state.rag_docs,
+        "rag_confidence": getattr(state, "rag_confidence", 0.0),
+        "rag_attempts": getattr(state, "rag_attempts", 0),
+        "previous_actions": [h.get("action") for h in state.reasoning_history],
+        "reasoning_history": state.reasoning_history,
+        "messages": state.messages,
+        "errors": state.errors
+    }
+
+    # 步骤2: 执行推理
+    result: ReasoningResult = await react_reason_async(state.user_query, context)
+
+    info(f"[推理] 推理结果: action={result.action.name}, confidence={result.confidence}")
+    if result.reasoning:
+        info(f"[推理] 推理过程: {result.reasoning}")
+
+    # 步骤3: 记录推理历史
+    state.reasoning_history.append({
+        "step": state.reasoning_step,
+        "action": result.action.name,
+        "confidence": result.confidence,
+        "reasoning": result.reasoning,
+        "timestamp": datetime.now().isoformat()
+    })
+
+    # 步骤4: 更新状态 - 只使用新的结构化字段
+    state.react_reasoning.last_reasoning = {
+        "action": result.action.name,
+        "confidence": result.confidence,
+        "reasoning": result.reasoning
+    }
+    state.react_reasoning.reasoning_result = result
+    state.last_action = result.action.name
+
+    # 步骤5: 发送推理事件
+    await dispatch_custom_event(
+        "react_reasoning",
+        make_react_event(
+            state.reasoning_step,
+            result.action.name,
+            result.confidence,
+            result.reasoning
+        ),
+        config
+    )
+
+    return state