M2b：删除旧 chat 体系——线性会话/叩心/情绪/纪念日模型与页面退役（迁移 003 双向验证），runs 去会话外键，测试全量修剪

backend/app/schemas/runtime.py

@@ -69,7 +69,6 @@ class RunResponse(BaseModel):
     character_id: str | None = Field(
         default=None, description="所属人物 ID；照心试演（kind=rehearsal）无正式人物。"
     )
-    session_id: str | None = Field(default=None, description="关联会话 ID。")
     status: str = Field(
         description="运行状态：queued / running / completed / failed / cancelled / interrupted。"
     )