feat(studio): R3 step_respond、运行页 UX 与 R4 思考流式

新增 worldbook 步骤 LLM 回复（thinking/draft/questions/evaluation），
运行页聊天区与产物/选项联动；评价区标签改为「评价与修改建议」；
流式开关开启时 NDJSON 推送思考内容，完成后拆分更新各字段。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/models/studio_models.py

@@ -159,8 +159,18 @@ class ToolQuestionOption(BaseModel):
     options: List[str] = Field(default_factory=list)
 
 
+class StepMessage(BaseModel):
+    """Short step-scoped dialogue (not full chat history)."""
+    id: str
+    role: str  # user | assistant
+    content: str
+    createdAt: Optional[str] = None
+
+
 class LastToolResponse(BaseModel):
     """LLM tool-call payload surfaced to the run UI (R2+)."""
+    thinking: Optional[str] = None
+    evaluation: Optional[str] = None
     questions: List[ToolQuestionOption] = Field(default_factory=list)
     generatedAt: Optional[str] = None
 
@@ -181,6 +191,7 @@ class StudioNodeRunState(BaseModel):
     loopUntilSatisfied: bool = False
     lastDraft: Optional[Dict[str, Any]] = None
     lastToolResponse: Optional[LastToolResponse] = None
+    stepMessages: List[StepMessage] = Field(default_factory=list)
 
 
 class StudioRun(BaseModel):
@@ -202,6 +213,13 @@ class AdvanceRunRequest(BaseModel):
     displayParams: Dict[str, str] = Field(default_factory=dict)
 
 
+class RunMessageRequest(BaseModel):
+    content: str = Field(..., min_length=1, max_length=32000)
+    stream: bool = False
+    profileId: Optional[str] = None
+    apiConfig: Optional[Dict[str, str]] = None
+
+
 class RenameRunRequest(BaseModel):
     title: str = Field(..., min_length=1, max_length=120)